We report a one-day-old Korean boy with 2-Methylbutyryl-CoA dehydrogenase(2-MBCDase) deficiency detected by urine organic acid and acylglycine analysis, plasma acylcarnitine analysis and confirmed by enzyme assay and Western blot. The patient was born at 35 weeks and three days with oligohydroamnios and premature rupture of membrane for 31 hours, as a second child of healthy non-consanguineous parents. There was no significant family history and spontaneous abortion. He was admitted at NICU under ventilator care due to prematurity, respiratory difficulty, and decreased generalized muscle tone. During the first week of hospitalization, he presented with disseminated intravascular coagulation and sepsis. A grade IV intraventricular hemorrhage on brain sonography was observed on the 7th day after birth with seizure. The clinical course of aggravation and recovery was repeated for one month. In laboratory tests, blood C5-acylcarnitines(isovaleryl/ methylbutyrylcarnitine) and urine 2-methylbutyrylglycine(2-MBG) were markedly elevated; butyrylglycine and isobutyrylglycine were also detected in small amounts in the urine. SBCAD(short branched-chain acyl-CoA dehydrogenase) enzyme activity was undetectable in cultured skin fibroblasts and Western blot showed no detectable immuno-reactive protein. Molecular analysis of the 2-MBCD gene revealed a polymorphism in the leader peptide region(38G>A; Arg13Lys) and homozygous for a non-coding polymorphism 639T>C. This is the first such case in Korea. This disorder is known to be relatively common in one other oriental ethnic group, the Hmong. The baby has been fed on a maple syrup urine disease(MSUD)-similar diet program, and is still alive and is 26-months-old now. However, he developed significant neurologic complications including communicating hydrocephalus, cerebral palsy, and blindness. Presumably the prematurity and its complications may also attribute to his severe neurologic problems. However, the clinical course was particularly severe, a finding in contrast with the observation from several asymptomatic Hmong cases. The clinical course of 2-MBCDase deficiency could be very variable and careful monitoring and follow up should be considered.