Citrullinemia is a rare inborn error of metabolism of the urea cycle, and was first reported by McMurray, et al. in 1962. It is inherited as an autosomal recessive trait. The normal synthesis of argininosuccinic acid is blocked in this disease due to a deficiency of argininosuccinic acid synthetase(AS), which has been demonstrated in liver cells and fibroblasts. The clinical symptoms are vomiting, lethargy or irritability, convulsion and mental retardation. The diagnosis is made by the finding of an increased plasma citrulline level. Every effort should be made to reduce the blood ammonia level as rapidly as possible before irreversible brain damage occurs. This report describes a case of citrullinemia that was diagnosed through organic acid analysis and amino acid analysis, and reviews the related literatures.