A 34 year-old man, who had been under care with diagnosis of Crohn's disease in the department of gastroenterology of our hospital since 1983, was referred to our urological clinic on May 21, 1987, because of right hydronephrosis found on ultrasonography. He did not complain of any urological symptoms. He underwent further roentgenographic examinations and a diagnosis of hydronephrosis complicated with Crohn's disease was made. On surgery of July 30, resection of ileocecal lesion, end-to-end ileocolostomy, right ureterolysis were performed. He is now visiting our clinic without recurrence of hydronephrosis up to present (7 months). In addition, we reviewed the 41 cases of urological disorders complicated with Crohn's disease in the literature reported in Japan. The cases were of vesicoenteric fistula including pericystitis (33 cases), hydronephrosis (10 cases), urolithiasis (2 cases) and ureterocolonic fistula (1 case). The patients were from 10 to 57 years (27.2 years in average) old. Sex distribution was uneven, 39 of patients were men and 2 were women. Urologic surgery was performed in almost all of the cases except for the patient with urolithiasis. All the patients having vesicoenteric fistula had urological complaints but the patients with hydronephrosis were relatively free from urological complaints. Thus, Crohn's disease has been recognized as an important gastrointestinal disease for urologists, and we will emphasize that periodical abdominal ultrasonography and urography for the patients with this disease should be necessary for checking up other complications such as hydronephrosis.