Hyperammonemic encephalopathy in urinary diversion with urea-splitting urinary tract infection. We present two cases of hyperammonemic encephalopathy secondary to urea-splitting urinary tract infection with urinary diversion. One patient had a ureterosigmoidostomy, the other an ileal loop diversion. Neither patient had significant underlying liver disease, but both had considerable muscle atrophy that may have predisposed them to develop hyperammonemia. Medical therapy did not provide long-term control of symptoms. In both cases, hyperammonemic encephalopathy resolved after revision of their urinary diversions. The probable mechanism of the metabolic derangements produced by urea-splitting urinary tract infections is reviewed. We suggest that patients with urinary diversion who develop hyperammonemic encephalopathy secondary to a urea-splitting urinary tract infection be treated with surgical revision of the urinary system to improve drainage and decrease bowel contact time. 