• Urinary diversion to the colon may produce a metabolic encephalopathy with elevated blood ammonia levels. The condition resembles hepatic encephalopathy but can occur without obvious liver disease. The patient described herein also had a computed tomographic scan showing diffuse brain swelling and superficial contrast enhancement. The condition responds rapidly to lowering of the blood ammonia level and requires a high level of suspicion for diagnosis in the patient who has undergone urinary diversion and has an unexplained metabolic encephalopathy.