The Authors report 4 girls with hypertransaminasemia and hepatic failure; in three patients the initial diagnosis was of unknown origin hepatitis, after the exclusion of the most frequent infectious and metabolic hepatic diseases; in one girl the assay of blood ammonia at the beginning oriented to an urea cycle disorder. Plasma ammonia, aminoacids and urinary orotic acid levels in all the patients agree with the diagnosis of Ornithine Transcarbamylase deficiency (OTCD), an X-linked inborn error of metabolism. The Authors also report the investigations in female subjects of the families with allopurinol challenge test and molecular study of DNA in two families. The Authors underline the importance of considering in patients with hepatic diseases an inborn error of metabolism; in girls with hepatic imbalance OTCD, a defect of the second step of the urea cycle, should always be taken into consideration.