Neurologic disease in glutaryl- CoA dehydrogenase (GC- DH)- deficiency usually presents with acute encephalopathic crises before 2 years of age. The authors report two previously asymptomatic patients with macro cephaly presenting with progressive neurologic deterioration and a severe leukoe ncephalopathy during adolescence or adulthood. Neurologic disease in glutaryl-CoA dehydrogenase (GC-DH) - deficiency usually presents with acute encephalopathic crises before 2 years of age. The authors report two previously asymptomatic patients with macro cephaly presenting with progressive neurologic deterioration and a severe leukoe ncephalopathy during adolescence or adulthood .