To define the prevalence of prostatic bacterial infection or colonization, tissue from 209 patients undergoing prostatectomy (204 transurethral and 5 suprapubic) was submitted for quantitative bacterial tissue cultures. Tissue from 44 patients (21 per cent) yielded positive, single organism bacterial growth. In an attempt to identify preoperatively this patient subgroup, multiple preoperative and intraoperative variables were examined. Although the presence of a preoperative indwelling catheter was associated with positive prostate cultures, only 34 per cent (24 of 70) of the patients with preoperative catheters had positive prostate cultures. Of the 44 patients with positive prostate cultures 36 (82 per cent) had sterile urine cultures documented preoperatively, all urine specimens having been obtained in the absence of antibiotics. The data support a significant prevalence (21 per cent or more) of prostatic infection in patients undergoing prostatic surgery for obstructive symptoms and an apparent paucity of reliable indicators by which to identify preoperatively this patient population.