Ornithine transcarbamylase deficiency is the most common urea cycle disorder in humans. It is inherited in an X-linked manner. The defective enzyme, ornithine transcarbamylase, is the final enzyme in the proximal portion of the urea cycle, responsible for converting carbamoyl phosphate and ornithine into citrullaine. In severe cases, rapidly increasing ammonia concentrations cause ataxia, lethargy and death without rapid intervention. This deficiency is diagnosed through clinical findings and biochemical testing, confirmed with molecular genetics techniques. Treatment aims to avoid precipitating increased ammonia levels. The most common treatment combines a low protein diet with nitrogen scavenging agents. Liver transplant is considered curative for this disease.