The urea cycle is the major metabolic pathway for excretion of waste nitrogen. Ornithine transcarbamylase deficiency is the most frequent urea cycle disorder. It is a hereditary-X-linked disease with over 150 mutations described. Ornithine transcarbamylase deficiency causes vomiting, lethargy, hyperventilation, and even death, mainly in the neonatal period. Ammonia, an extremely toxic molecule for the organism, is generated during protein catabolism and is accumulated in patients with this deficiency. Part of the treatment consists of a low-protein diet, to avoid hyperammonemia episodes, which can even have a fatal outcome. Patients can become deficient in several amino acids, either through the low-protein diet or directly through the primary enzyme deficiency; this in turn can cause an acrodermatitis enteropathica-like dermatosis.