The aim of this study was to determine the prevalence and type of symptomatic anal and perianal diseases in patients belonging to group IV of the Centers for Disease Control classification of infections with human immuno-deficiency virus. Among the 190 prospectively included patients, 31 (16.3 percent) (30 men, 29 homosexuals or bisexuals; 1 woman) had anal symptoms and were referred for proctological examination. Thirty-five "specific" diagnoses were reached in 25 (13.2 percent) patients: 21 ulcerations, 7 condyloma acuminata, 6 perianal sepsis and 1 non-Hodgkin malignant lymphoma. The causes of ulcerations were 16 herpes, one syphilitic chancre and one fissure-in-ano. Three ulcerations remained unexplained despite bacteriological, viral, and histological investigations. Eight patients underwent 10 surgical procedures without significantly delayed wound healing.