Mycological, cultural and/or serological studies were performed on 98 patients hospitalized in the Department of Infectious Diseases of the Catholic University in Rome with diagnoses of acquired immune deficiency syndrome (AIDS) or AIDS-related complex (ARC) diseases. The incidence of mycoses was evaluated by retrospectively analyzing the results of mycological examinations and comparing them with clinical manifestations. The presence of concomitant bacterial, viral and parasitic infections was also examined. For epidemiological purposes, the study was extended to include the biotyping of all yeasts isolated from patients hospitalized between September 1988 and February 1989 in the same Department. Antimycotic susceptibility was also determined for the first yeast isolate obtained from each of these patients. Oral candidiasis (50 cases) caused by Candida albicans was the most frequent mycosis, followed by esophageal candidiasis (13 cases) and cryptococcosis (6 cases). Four out of the 6 cryptococcosis patients had meningeal involvement. Systemic candidiasis (2 cases) and aspergillosis (1 case) were less common. Biotyping of yeasts isolated between September 1988 and February 1989 with the killer system revealed type 377 to be the most common among the C. albicans isolates. It represented 70% of all the yeasts isolated.