The prevalence of viral and bacterial sexually transmitted diseases were studied in 101 men attending a dermatovenereal outpatient clinic in Mogadishu. A control group of 103 healthy adult men were included for the serological part of the study. Serological markers of hepatitis B virus (HBV), human immunodeficiency virus (HIV), cytomegalovirus (CMV) and herpes simplex virus (HSV) were studied. All sera were tested for syphilis markers. HBV serum markers were detected in 84% of the men in the study group and 66% of the healthy controls (P less than 0.005). Hepatitis B virus carriers were detected more frequently in the study group than among the controls. Also, 96% of the men in both groups had CMV antibodies and all of them had antibodies to HSV. No sera were found to contain HIV antibodies. The TPHA-positivity was 10% and 3% in the study and control groups respectively, and 5% of the patients had syphilis IgM antibodies. Sexual contact with prostitutes was recorded in 54% and 48% respectively of patients and controls, and such contact was correlated with TPHA-positivity in the study group. Chlamydia trachomatis antigen was detected in urogenital specimens of 14% of the men in the study group and gonococcal culture was positive in 53% of those with urethral discharge.