Cystoscopic and histologic evidence of polypoid cystitis was recorded in 20 hospitalized patients with indwelling urethral catheters followed by cystoscopy, biopsies and repeated urine samples before and after catheter removal. The majority of the lesions were located in the posterior wall or dome. The lesions disappeared after removal of the catheter in 13 of the 15 patients followed for up to 28 weeks despite persistent bacteriuria. Polypoid cystitis still remained 28 weeks after catheter removal in 1 patient. The lesion is important as a differential diagnosis to bladder tumor. The importance of adequate biopsies is emphasized.