A 5-month-old Korean boy who presented with lethargy and cardiomyopathy was diagnosed with very long chain acyl coenzyme A dehydrogenase (VLCAD) deficiency by organic acid, fatty acid, acylcarnitine, and molecular genetic analysis. The patient was a compound heterozygote for mutations in the VLCAD gene. One allele contains a 3-bp deletion in exon 6, deleting glutamic acid in codon 130 (E130del ); this allele is of paternal origin. The patient's maternally derived allele is a novel mutation, C1843T in exon 20, which creates a premature termination codon (R615stop ). Although molecular genetic characterization of VLCAD deficiency is limited to a few patients, heterogeneity of mutations is already apparent. However, the E130del is a relatively frequent mutant allele, which has been noted in 2 previously identified patients. The 2 mutant alleles in our patient appear to be responsible for his severe and fatal clinical manifestations.