In January 1982, the Centers for Disease Control began a prospective study of unexplained generalized lymphadenopathy syndrome in 78 homosexual or bisexual men. As of Aug 1, 1984, the median durations of lymphadenopathy and enrollment were 29.5 months and 20 months, respectively. Antibodies to human T-cell lymphotropic virus type III/ lymphadenopathy-associated virus were present in 75 (96%) of the study patients. Five (6%) of the patients were diagnosed as having the acquired immunodeficiency syndrome five to 25 months after the onset of lymphadenopathy. At the time of their initial visit, these five patients had lower T-helper cell counts, hematocrits, lymphocyte counts, and pokeweed mitogen stimulation ratios and were more likely to report severe symptoms than patients who did not develop the acquired immunodeficiency syndrome. During 318 follow-up visits, except for the development of the acquired immunodeficiency syndrome in five patients, there has been little change in the initial laboratory and clinical measures of this cohort. Within the follow-up period of this study, the features of lymphadenopathy syndrome have been unremitting for the majority of patients. (JAMA1985;254:930-935)