The possibility that after T.U.R. of superficial bladder tumors, some fragments remain unresected, or that local metastases may have gone unnoticed during surgery which may later be interpreted as early relapses of the original tumor, has led us to assess urine cytology taken through early bladder lavage after T.U.R. as a means to control complete removal of tumors during endoscopic surgery. After comparing cytologic results with cystoscopic and biopsy findings, it was found that the sensitivity of the method increased progressively with the degree and staging of the original lesion, with "in situ" carcinomas presenting the highest percentages relating to low grade cytology due to the great similarity these cells have with those of urothelial repair. The best time to obtain samples for cytologic study is at the withdrawal of the catheter, coinciding with cessation of hematuria.