A 26-year-old man was referred to our hospital for further evaluation of a cystic lesion in the pelvis. He was completely asymptomatic, although he experienced gross hematuria 10 months before his visit. Drip infusion pyelography (DIP) and abdominal computerized tomography (CT) showed a cystic structure behind the bladder and absence of the left kidney. Transrectal ultrasonography (TRUS) suggested left ejaculatory duct obstruction and seminal vesicle deformity. On cystoscopy a large bulging mass under the left side of the bladder was seen. The left half of the trigone and left ureteral orifice were absent. Vasovesiculography demonstrated dilated and tortuous left seminal vesicle. Three days after this procedure, the patient suffered left epididymitis. It did not respond rapidly to antibiotic therapy, so percutaneous drainage of the cyst was performed. He has been completely free of symptoms and no seminal vesicle cysts have been detected on TRUS at five months follow-up.