To identify and describe a subgroup of men infected with HIV for 10-15 years without immunologic progression, and to evaluate the effect of sexually transmitted diseases (STD) and recreational drug use on delayed HIV disease progression. Inception cohort study. Municipal STD clinic. A total of 588 men with well documented dates of HIV seroconversion and 197 HIV-seronegative controls. AIDS, CD4+ count, rate of CD4+ cell loss, CD8+ count, beta 2-microglobulin, complete blood count, p24 antigen and HIV-related symptoms. Of 588 men, 69% had developed AIDS by 14 years after HIV seroconversion (95% confidence interval, 64-73%). Of 539 men with HIV seroconversion dates prior to 1983, 42 men (8%) were healthy long-term HIV-positives (HLP), HIV-infected > or = 10 years without AIDS and with CD4+ counts > 500 x 10(6)/l. When compared with progressors (men with HIV seroconversion prior to 1983 but with AIDS or CD4+ counts < 200 x 10(6)/l), HLP had a significantly slower rate of CD4+ decline (6 versus 85 x 10(6)/l cells/year), and less abnormal immunologic, hematologic and clinical parameters. However, when compared with HIV-uninfected controls, HLP demonstrated lower CD4+ counts and mild hematologic abnormalities. There were no consistent differences between HLP and progressors in prior exposure to recreational drugs or STD. There are individuals with long-term HIV infection who appear clinically and immunologically healthy 10-15 years after HIV seroconversion, with stable CD4+ counts. Lack of exposure to STD or recreational drugs does not appear to explain the delayed course of disease progression in HLP.