From July, 1990 to June, 1991, a prospective study was conducted on 65 patients with infiltrating bladder tumor to determine the possibility of distinguishing T2 from T3 tumors endoscopically. Sixty-six tumors were resected, including all of the bladder wall, and samples of perivesical fat were obtained from the tumor bed. The pathologist found infiltration of the bladder muscle wall in 50 cases (75.6%) and classified 12 tumors as T2 and 38 as T3. Fifty-five per cent of the T3a tumors were reclassified as T3b on the basis of the indirect signs of the pelvic scan and bimanual palpation performed under anesthesia. The clinical staging correlated with the pathological findings in 52.6% of the 19 cases of pT3b that underwent radical cystoprostatectomy; 31.7% of the pT3b tumors were clinically understaged, mainly due to prostatic infiltration. We can conclude from our findings that the differential diagnosis between pT2 and pT3 tumors is possible by endoscopic resection for most of the infiltrating bladder tumors; however, pT3a tumors cannot be distinguished from pT3b tumors with sufficient reliability.