UCDs are among the most common inherited metabolic diseases in Japan. We investigated the clinical manifestations, treatment, and prognoses of 177 patients with UCDs who were evaluated and treated from January 1999 to March 2009 in Japan, using a questionnaire survey. Among these 177 patients, 42 (seven with carbamoyl phosphate synthetase 1 deficiency, 27 with ornithine transcarbamylase deficiency, seven with argininosuccinate synthetase deficiency, and one with arginase 1 deficiency) underwent living-donor LT. Although this study was retrospective and included limited neurodevelopmental information before and after LT, we evaluated whether LT could improve neurodevelopmental outcomes in patients with UCDs. The neurodevelopmental outcomes of patients with a MAC of <300 μmol/L at the time of onset were not significantly different between the LT and non-LT groups (P=.222). LT may have prevented further neurodevelopmental complications in children with MAC ≥300 μmol/L (P=.008) compared with non-transplant management. Therefore, Liver transplant should be considered in patients with UCD with a MAC of ≥300 μmol/L at the time of disease onset.