A transurethral resection of the prostate (TURP) is often performed to treat benign prostatic hypertrophy or prostatic carcinoma. Transurethral resection syndrome (TURS) is a rare but serious complication of TURP that has two different causes: (1) intravascular absorption of the irrigation fluid through the open prostatic venous sinus (TURP syndrome); and (2) intraperitoneal extravasation of the irrigation fluid through perforation of the bladder. In general, a laparotomy, repair of injury, or conservative approach such as bladder drainage, percutaneous drainage of the abdomen combined with medical treatment are performed to manage TURS attributed to the latter mechanism. We report a patient with TURS, who showed a gradual onset of hyponatremia after bladder perforation and intraperitoneal extravasation of the irrigation fluid, and was treated successfully using a conservative approach.