Seventy-five homosexual men with generalized lymphadenopathy for at least three months (lymphadenopathy syndrome [LAS]), subsequently shown to be seropositive for antibody against human immunodeficiency virus, were enrolled in a prospective study in Atlanta in 1982 and 1983. As of Nov 30,1987, twenty-two (29%) of the 75 were known to have developed acquired immunodeficiency syndrome (AIDS) three to 60 months after enrollment and five to 69 months after onset of LAS. The six-year cumulative incidence of AIDS, by Kaplan-Meier survival analysis, was 38%. The cumulative incidence in years 4,5, and 6 (30%) was significantly higher than in years 1, 2, and 3 (11%), suggesting that the risk for AIDS increases after the third year of LAS and that many more study participants will eventually develop AIDS. A precipitous decline in the T-helper cell count frequently heralds the diagnosis of AIDS; this decrease appears to occur at different times after the onset of LAS in different persons. The four-year cumulative incidence of AIDS following observations of T-helper cell counts less than 200/mm3, 200 to 299/mm3, 300 to 399/mm3, and 400/mm3or greater was 84%, 41%, 25%, and 18%, respectively; these data are important for determining prognosis in the individual patient as well as for determining the suitability of candidates and baseline data for drug trials. (JAMA1988;260:2694-2697)