A total of 33 patients were diagnosed with a UCD at La Paz University Hospital between January 2000 and December 2021 with the following diagnosis: 20 ornithine transcarbamylase deficiency (OTC), 6 argininosuccinate synthetase deficiency (ASD), 4 carbamylphosphate synthetase 1 deficiency (CPS1), 2 argininosuccinate lyase deficiency (ASL) and 1 N-acetylglutamate synthetase deficiency (NAGS). Here, CPS1 is linked to citrullinemia type I.