Newborn was referred with diagnosis of neonatal epilepsy. Medical team could suspect and confirm D-bifunctional peroxisomal enzymatic deficiency diagnosis. It was made by family antecedents, severe neonatal hypotonia, uncontrolled neonatal seizures, craniofacial dysmorphic features, psychomotor retardation, neuronal migration defect and a positive peroxisomal panel. The full study in skin fibroblasts involved enzyme analysis, complementation studies and DNA analysis. The accumulation of very long chain fatty acids, partial deficiency in phytanic acid oxidation, and abnormal morphology of peroxisomes was consistent with a defect in peroxisomal fatty acid oxidation, involving D-bifunctional protein. It is very important to make a diagnosis of this innate error of metabolism in order to give preconceptional genetic counseling, to identify recurrence risk and to perform mutation analysis for the D-bifunctional protein gene, and to offer the prenatal diagnosis.