Nosocomial urinary tract infections (UTI) are frequent complications after transurethral prostatectomy. The resection itself, postoperative catheterization and the prostate are possible causes of these infections. In this prospective study we investigated the influence of bacterial prostatic colonization on the incidence of postoperative urinary tract infections and inflammatory complications. In 78 patients we observed in 42 cases (53.8%) a bacterial prostatitis. In 14 patients (17.9%) we found nosocomial UTI's and in 12 patients (15.4%) inflammatory complications. The incidence of postoperative UTI's increase significantly in patients with positive prostate-cultures. On the other hand we only found corresponding prostate- and postoperative urine-cultures in less than 50%. The presented data are not sufficient to conclude the kind of relevance of bacterial prostatic colonization for postoperative UTI's in transurethral prostatectomy. Under consideration of the significant increase of nosocomial UTI's in patients with positive prostate cultures a perioperative antibiotic prophylaxis seems to be required in general.