A female Japanese patient diagnosed with peroxisome biogenesis defect (PBD), who had hypotonia and craniofacial dysmorphism, was given supplementation of docosahexaenoic acid (DHA). Accumulation of very long chain fatty acids was revealed, and a diagnosis of PBD was made at 2 months of age because of the absence of peroxisomes, a defect in peroxisomal beta-oxidation enzymes and a decreased level of DHA in the erythrocytes. Supplementation of DHA was introduced at 3 months of age. For the first several months, psychomotor development was fairly good. The patient could laugh, brush off a blanket and play with toys at 6 months of age. However, neurological regression and convulsions occurred after 7 months of age. After recurrent respiratory infections and disturbance of the circadian rhythm, the patient died of liver failure and disseminated intravascular coagulopathy at 20 months of age. DHA may have a favorable effect on the early development of patients with PBD, but neurological deterioration cannot be prevented. Patients with a milder phenotype would be better candidates for DHA supplementation.