It has been difficult to make a correct diagnosis in B.P.H.. For the clinical signs are nonspecific anddigital examination is not reliable owing to the variation of each prostatic state and the clinician's feelings.Even in the radiological methods, there have been no criteria to confirm the diagnosis. We have noticed that thereis a significant difference of the prostatic urethral lengths between those of the B.P.H. patients and normalindividuals in cystourethrograms based on 53 known B.P.H. cases that were confirmed by postoperative biopsies. Itwill be the most valuable to measure the prostatic urethral length for the correct preoperative diagnosis ofB.P.H.