Although Seventh-Day Adventism espouses basic Christian doctrines--belief in the Trinity, the virgin birth and Resurrection of Christ, the Bible as the word of God--and is considered by some "main line" Christians to be simply another Protestant denomination, it is distinguished by a number of points that justify its classification as a cult.
The word "adventist" derives from the Latin, adventus
-"coming"--and refers to those groups that not only expect the
imminent return of Christ, but have at different times tried to predict the
years and even the day of this return--in spite of the Lord's warning: But of that
day and hour known to no man, not the angels of heaven, but my Father only
(Matt. 24:36). Although "adventism" is now a familiar theme among many
Protestant groups, particularly those that come under the
"Pentecostal" umbrella, the Adventist movement originated in the 19th
century on the basis of attempts to make precise predictions about the Second
Adventists--and there are several groups in addition to the Seventh-Day Adventists -- originated with William Miller, a farmer who was born in Massachusetts shortly after the American Revolution. Although he lost his faith in God as a teenager, he came to believe once again at the age of 37, returning to the Baptist faith of his parents following a time of intense study of the Bible.
His interest focussed on biblical prophecies contained in the Books of Daniel and Revelation. Based on his interpretation of the passage 2300 evenings and mornings (Daniel 8:14), Miller announced m 1831 that Christ would return to the earth between March of 1843 and March of 1844. Although at this time he still remained a Baptist, Miller began to gather a number of converts to his views, and launched the first Adventist publication, a newspaper called "Signs of the Times."
Miller was not the only "end time" prophet of his day. Early 19th century New England abounded in a great variety of preachers, and the popularity of camp revival meetings provided them with a ready audience for their eschatological pronouncements. At these gatherings religious emotionalism often ran high. Miller, a straightforward and earnest if undistinguished speaker who appears lo have been free of undue ambition, was distressed at the fanaticism of some of his followers: "their meetings seemed to him 'more like Babel than a solemn assembly of penitents bowing in humble reverence before a holy God”  Some 200 preachers helped to promote Miller's views in a national crusade, and by 1840 they had attracted an estimated 50,000 followers, called 'Millerites'.
When Christ did not return during the predicted year, Miller confessed his error, but one of his disciples "re-calculated" the time of the Second Coming for October 22, 1844.  So intense was their expectation that when the "Great Disappointment' came, a number of Millerites went insane and some even committed suicide, although most simply rejoined their former denominations.
This did not, however, spell the end of the movement. The morning after the Great Disappointment, a devoted Millerite by the name of Hiram Edson had a vision of heaven: "He saw that the cleansing of the sanctuary foretold in Daniel did not coincide with the Second Coming but rather with Christ's entry into the most holy place of the heavenly sanctuary just prior to his return.' 
Meanwhile, another Millerite, Joseph Bates, had become convinced that the holy day of the week was Saturday, the Sabbath, and that this day, rather than Sunday, should be observed.  This seemingly novel teaching among Protestants was in fact borrowed from the Seventh Day Baptists. It was officially condemned by the moderate wing of Millerites in 1845, but the very next year it was promoted by a smaller group under the influence of a young “prophetess," Ellen G. Harmon Shortly after meeting Bates in 1846, she had had a vision: "In heaven, she said, Hesus had allowed her to see the tables of stone on which the Ten Commandments were inscribed. To her amazement, the fourth commandment, requiring observance of the seventh day, was in the very center of the ten precepts, with a soft halo of light encircling it’. 
Later that year, the 19 year old Ellen married James White, an Adventist preacher. Subsequently, she had a revelation which elaborated upon Edson's vision. She announced that in 1844 the Lord had "entered the sanctuary of Heaven in order to cleanse the earth of the grievous sin of profaning the Sabbath. He would return to earth when this task was accomplished . 
This wedding of the sabbatarian and Adventist views provided the foundation for the organization of this particular brand of Millerites as the Seventh-Day Adventists, a name officially adopted in 1860. Cementing this new denomination was the recognition of Ellen G. White as a divinely inspired prophetess whose authority was equal to that of the Old Testament prophets. Indeed, by this time Miller had long since retired from active leadership in the movement, which in a very short period of time had passed to James White and, more particularly, his wife. It is she who is considered to be the foundress of Seventh-Day Advcntism, and in spite of Adventist claims to believe the Bible and only the Bible, it is Mrs. White's book---she was a prolific writer-- which are considered by Adventists to be the primary and authoritative commentary on Scripture and in practice are held above Scripture where the two conflict.
The Adventists’ obsessive emphasis on keeping the Sabbath (a point they have made into a "test' of a true Christian) and on the end times, show there to be like most sects singling out one or two thee logical issues that become the raison d'etre of the whole movement. Their greatest error, however, lies in their implicit trust of Ellen G. White. Not only are her writings full of glaring contradictions, but, what is worse, scholarship was clearly revealed several in stances of plagiarism in her "divinely inspired Testimonies'. To cite some examples:
In December, 1844, she had a vision in which it was made clear to her that on October 22 God had closed the door of salvation to sinners (those who had not yet accepted the Millerite teachings). In subsequent collections of her early writings, however, references to this shut door view were deleted. Likewise, at one time she claimed that to resort to physicians signalled a lack of faith; one should trust one's health to God alone. A few years later, however, she wrote that 'in some cases the counsel of an earthly physician is very necessary. This position we have always held.  A similar about-face was made in respect to her "divine revelation" on dress reform, a hot topic of the day thanks to early feminists who had adopted a shorter skirt over pants or bloomers as their uniform. In 1863 Ellen G. White stated that "God would not have His people adopt the reform dress," while four years later she declared: 'God would now have His people adopt the reform dress," claiming that the pattern for such a proper fashion of dress had been revealed to her in a vision in 1863! In spite of this testimony, Mrs, White's efforts to press her model of dress unto her Adventist sisters were unsuccessful, and she herself was greatly "relieved when, in 1875, she had a revelation that the dress reform had become "an injury to the cause of truth" and she could in clear conscience lay it to rest.
Dress reform was part of the broader issue of health reform, a subjet which enjoyed considerable attention in the early and mid 1800's. The medical profession at that time still relied on primitive---and often ineffectual--practices such as leeching, and there was considerable room for new ideas, even from those who had little or no formal medical training. Mrs White had had great success as a speaker on the temperance wagon--a rallying point for most revivalists of the day--and it was not long before she extended her prohibition of alcohol to stimulants: tea coffee, cocoa, tobacco. Later, in 1863, she had a vision which inspired her to add meat, eggs, butter and cheese to her list of proscribed foods. Health reform, she claimed, was "as closely connected with present truth as the arm is connected with the body
She and her husband both suffered from chronic ill health, and it is hardly surprising that health began to figure prominently in her theology. Even contemporaries, however, could not help noticing striking parallels between her 'divinely inspired" pronouncements on the subject and the ideas promoted by some of the leading health reformers of the day notably those which appeared in L.B. Coles's Philosophy of Health. One of her literary assistants, Frances Bolton, finally complained to a fellow Adventist: "Most of what I write is published in the Review and Herald as having come from the pen of Sister White under inspiration of God. I want to tell you that I am greatly distressed over this matter for I feel that I am acting a deceptive part."  When knowledge of this admission reached Mrs. White, Miss Bolton was summarily relieved of her post.
Gradual disclosures of this nature forced a schism in the Adventist ranks, but even charges of plagiarism were not enough to shake the confidence most Adventists placed in their guiding prophetess. In any case, under her direction they continued to establish health institutes and sanatoriums in various parts of this country and abroad. In 1910 one of these sanatoriums, in Loma Linda California, opened its doors as the College of Medical Evangelists.  Today numerous hospitals around the country are operated by the Adventists. Cafeterias in these institutions offer only vegetarian meals (the most devout Adventists are vegetarians, and consumption of coffee, tea, and alcohol are forbidden), and hospital chaplains offer spiritual comfort and guidance to patients based upon the writings of Ellen G. White, whose books are made available. Many of these hospitals combine traditional patient-care with special cancer wards, hospice and drug/alcohol abuse programs, ,schools for the young, and a church.
In addition to their doctrines concerning the Second Coming and the Sabbath, Seventh-Day Adventists teach that man does not have an immortal soul. At death he simply ceases to exist until Christ on the Last Day resurrects the body and at that time endows it with an immortal soul. They also believe in the complete extinction of the unrighteous (i.e., they will not suffer everlasting torment).
International headquarters for the 'World Federation of Seventh-Day Adventists" is located near Washington, D.C. A world-wide membership of nearly four million, organized m thirteen "divisions," is governed in all matters by a democratically chosen "General Conference."
Although Seventh-Day Adventists are not aggressive proselytizers in the manner of Mormons or Jehovah's Witnesses, they are intensely missionary. They "do not regard themselves as simply one more church body in the world, but as a prophetic movement having the everlasting gospel to proclaim m what they believe to be the setting of the hour of God's judgment.'  As missionaries Adventists reach many people through their somewhat sophisticated television programming--especially the weekly "It is Written." The widely circulated magazine Plain Truth is published by an Adventist off-shoot, the Worldwide Church of God, and is distributed free, of charge, supported by the tithes of the Church's members, although the Church itself is rarely mentioned in the publication. This "tactic of camouflaging their identity in the media"  is characteristic of cults,
The Adventists' emphasis on traditional family values and health makes
them extremely' attractive to those who are disturbed by the modern
disintegration of the family and the gradual poisoning of our national food
supply. Theologically, however, their arguments are not difficult to refute (or
those with a sound knowledge of Scripture and Church history.
Fr. Alexey Young
 Ronald L. Numbers, Prophetess ofHealth: A Study of Ellen G. White, Harper & Row, 1976, iv 16
 Scholars dispute the validity of stories that they dressed up in special 'ascension' robes and waited on hilltops.
 Ibid., p 13.
 Adventists routinely tell prospective converts that it was the Emperor Constantine who "changed the Sabbath to Sunday,' a violation of God's commandment and a grievous blasphemy. In fact, however, early Christians worshipped on Sunday which they regarded as the 'Lord's Day"--the day of theLord's Resurrection, while Saturday remained the Sabbath Day. Orthodox Christians, in observance of this fact, try wherever possible (usually only at monasteries and large cathedrals, these days) to serve Divine Liturgy on Saturday as well as Sunday. In addition, during the lenten seasons, the fast is slightly relaxed on both these days.
 Ibid., iv. 15.
 Konrad Algermissen, Christian Sects.
 Quoted in Numbers, p. 36.
 Quoted in Numbers, p. 195
 This center later developed a
commercial branch, Loma Linda Foods, providing numerous 'meat substitutes' for
Adventists and vegetarians in general. Many Orthodox Christians have discovered
the usefulness of these products on fast days.
 LeRoy E. Froom, 'Seventh-Day Adventists" in The American Protestant Heritage, edited by V. Ferm, Philosophical Library, 1953, p 376
 Kenneth Boa, Cults, World Religions, and You, Victor Books, 1960, p 92.[OA/_private/oabot.htm]