To establish the prevalence of HIV-related oral lesions, we performed oral examinations of members of three San Francisco epidemiological cohorts of homosexual and bisexual men over a 3-year period. Hairy leukoplakia, pseudomembranous and erythematous candidiasis, angular cheilitis, Kaposi's sarcoma, and oral ulcers were more common in HIV-infected subjects than in HIV-negative subjects. Among HIV-infected individuals, hairy leukoplakia was the most common lesion [20.4%, 95% confidence interval (CI) 17.5-23.3%] and pseudomembranous candidiasis was the next most common (5.8%, 95% CI 4.1-7.5%). Hairy leukoplakia, pseudomembranous candidiasis, angular cheilitis and Kaposi's sarcoma were significantly more common in patients with lower CD4 lymphocyte counts (P less than 0.05). The prevalence of erythematous candidiasis and Kaposi's sarcoma increased during the 3-year period. Careful oral examinations may identify infected patients and provide suggestive information concerning their immune status.