Maple syrup urine disease (MSUD), or branched-chain ketoaciduria, is an autosomal recessive disorder of branched-chain amino acid metabolism. The classic MSUD is the most severe form. The prognosis is usually guarded. The acute metabolic decompensation and neurological deterioration attribute to severe sequelae. The age of diagnosis and subsequent metabolic control are the most important determinants of long-term prognosis. We report one classic MSUD case with good outcome. The early diagnosis was achieved by tandem mass spectrometry screening. Since most MSUD patients in Taiwan are native Taiwanese, we strongly suggest routine tandem mass screening of MSUD is necessary, especially in the high-risk groups, to minimize morbidity and mortality.