The cases of 90 homosexual or bisexual men with generalized lymphadenopathy were studied by epidemiologic, clinical, pathologic, immunologic, and genetic methods. The patients ranged in age from 20 to 52 years and had histories of multiple sexually transmitted diseases and both recreational and prescription drug use. Histologically, their lymph nodes showed three patterns: explosive follicular hyperplasia; follicular involution with expansion of the paracortical area; and a mixed pattern of follicular hyperplasia and follicular involution in the same lymph node. The frequency of HLA-DR5 was significantly increased in these patients (p less than 0.005) compared with that in controls. All patients had impaired cell-mediated immunity. Opportunistic infections, lymphomas, or Kaposi's sarcoma subsequently developed in 15 patients who had had severe immune dysfunction for the previous 3 to 13 months. We suggest that generalized lymphadenopathy is part of the spectrum of a disorder manifested by acquired immunodeficiency, opportunistic infections, Kaposi's sarcoma, and malignant lymphomas.