We used structured diagnostic interviews and rating scales to assess lifetime prevalence of psychiatric disorders, by DSM-III criteria, among an unselected sample of 56 ambulatory homosexual men in four groups: men with acquired immunodeficiency syndrome (AIDS), men with AIDS-related complex (ARC), men asymptomatic or mildly symptomatic but seropositive for antibody to human immunodeficiency virus (HIV), and HIV-seronegative men. An age- and demographically matched comparison group of 22 healthy, heterosexual controls was also studied. The homosexual men had lifetime rates of alcohol or nonopiate drug abuse (22/56 [39.3%]), generalized anxiety disorder (22/56 [39.3%]), and major depression (17/56 [30.3%]) that often preceded diagnosed medical illness or knowledge of HIV status. The six-month point prevalence of these disorders in homosexual men was also high, especially alcohol abuse in patients with AIDS-related complex, and the occurrence of a DSM-III disorder within the previous six months significantly exceeded that in heterosexual controls. The data suggest that there may be a higher prevalence of anxiety disorder and major depressive illness in homosexual men when compared with sociodemographically matched heterosexual men and that the psychiatric morbidity may have preceded the onset of the AIDS epidemic. These findings indicate that awareness of psychiatric history is necessary to comprehensive medical care of men at high risk for AIDS, even among relatively healthy outpatients.