3-Hydroxyacyl-CoA dehydrogenase (HADH, SCHAD) deficiency is an autosomal recessive metabolic disorder, resulting from mutations in the HADH gene. HADH deficiency is one of the mitochondrial fatty acid oxidation disorders that has been the most recently described only in a few patients. The clinical phenotype of most patients that have been described is recurrent hypoglycemia associated with hyperinsulinism.