Between April 1984 and December 1985, 50 patients diagnosed as AIDS were observed in our Clinic. Risk factors were homosexuality in 21 cases (42%), drug addiction in 20 (40%), homosexuality and drug addiction in 3 (6%), haemophilia in 1 (2%). In the remaining 5 cases the infection was acquired by vertical transmission in 2 (4%), by promiscuous heterosexual intercourse in 2 (4%) and by a single blood transfusion in 1 (2%). Kaposi's sarcoma (KS) was the main clinical feature in 8 patients, although associated with opportunistic infections (OI) in 7 of them. A total of 91 different OI were diagnosed with a noteworthy prevalence of mycotic infections compared with OI due to other micro-organisms: 40 deep mycoses by Candida albicans, and 5 cryptococcoses. Pneumocystis carinii pneumonia (PCP) was diagnosed in 20 patients. Our data differ from the ones collected in the USA both epidemiologically, since we observed a greater incidence of AIDS in drug-addicts than in homosexuals and clinically, since in Italy a lower rate of neoplastic disease and, conversely, a higher rate of OI other than PCP are reported.