Bacterial prostatitis was diagnosed in 17 of 209 human immunodeficiency virus-infected men hospitalized from October 1985 to October 1987. A history of urogenital disease was found in 13 of 17 patients. Clinical signs of prostatitis were present in 16 of 17 patients, including fever in 13, urinary symptoms in 11 and tender prostate on rectal palpation in 7. Bacteriuria was found in 14 of the 17 patients. Prostatic ultrasound examination showed an abscess in 11 of 16 patients studied. Prostatitis was diagnosed at autopsy in 1 patient. Within 6 weeks after onset of antimicrobial therapy 9 of 13 patients were cured and 4 of 13 did not respond to therapy. Among the 7 patients followed for more than 2 months after the end of antimicrobial therapy 5 had relapse. The prevalence of bacterial prostatitis among human immunodeficiency virus-infected patients increased from 3 per cent in asymptomatic human immunodeficiency virus-infected patients to 14 per cent in patients with the acquired immunodeficiency syndrome.