Urethral stricture, a serious and peculiar condition, has hitherto been regarded as being a complication of severe gonorrheal infection or resulting from unusual traumas. It has, therefore, been thought that the condition would decrease if gonorrhea were prevented or cured. In the medical literature of Japan and abroad, no systematic studies, aside from statistical observations, have been published. However, the existence of this condition still persists today and the patients suffering from it are as numerous and pitiful as in the past. The author has for many years been investigating this problem under the supervision of Prof. Tabayashi and the results so far obtained, though by no means complete, are here presented.The materials used in this study include 122 cases of urethral stricture, of which 31 patients have been treated by surgical operations. The urethral tissues involving the stricture were removed and the specimens were studied from many angles in serial sections. Hence, the present observations and discussions are based chiefly on the histological changes consequent to the stricture.1. Etiology. The most frequently cited cause of urethral stricture in the literature is gonorrhea in nearly all cases, together with a few which resulted from trauma or from undue manipulations at the time of operations. Gonorrhea, trauma or tuberculosis as causes of stricture have thus been considered to be the main causes of urethral stricture, but in the author's study a fourth distinct cause has been discovered, which is rather difficult to define but quite characteristic and even specific. Gonorrhea responds to chemotherapy and this fact naturally reduces the incidence as well as complications of stricture. Trauma, on the other hand, shows a tendency to increase because of multiplying occupational hazards associated with development of heavy industry and skyscraper construction, dissemination of high speed vehicles and utilization of stones and procelains in buildings and furnitures. There is a certain number of patients with stricture of non-specific and not cleary definable cause. Tuberculosis constitutes approximately one-third of the causes of stricture, as with trauma and gonorrhea, according to statistical surveys. There is little doubt that some discrepacies are bound to enter into such statistics according to the environmental influences. In any case, the most predominant cause is gonorrhea, followed by trauma, and not a few due to an unknown but rather specific cause. Tuberculosis, though definite in etiological relationship, plays only a minor role.2. Incidence. The total number of 122 cases here studies represents an incidence of only 1.44 per cent of the 8, 432 patients treated in our department, which is probably the lowest figure ever reported in the literature at present. The cause in these cases include gonorrhea 69.67 per cent, trauma 16.39 per cent, unknown cause 9.01 per cent and tuberculosis 4.91 per cent, excluding those due to congenital anomalies, operative complications or urethral stones.3. Location. The location of stricture is customarily described either by anatomical designation or by measurement of distance from the external urethral orifice, but these methods are complicated and often inaccurate. In the majority of cases the present practice is to determine by urethrography, and, utilizing this method, the author simply distinguishes the locations as anterior urethra, bulbo-membranous urethra and membranous-prostatic urethra. However, the stricture occurring in the portion between the internal orifice and prostate as well as the one situated at the external orifice have been excluded, since the former is difficult to be differentiated from prostatic hypertrophy, while the latter comprises many instances of congenital defect.