Glutaric aciduria type I is an uncommon inborn error of metabolism. It is a serious disease, often with a fatal outcome. Magnetic resonance imaging findings and the clinical course of monozygotic twin females with glutaric aciduria type I who were admitted with acute encephalopathic crisis symptoms 3 days after immunization for poliovirus are presented in this report. Magnetic resonance imaging findings revealed hyper-intensity in the putamen, head of the left caudate nucleus, and globus pallidus, periventricular white matter (on T-2-weighted images), arachnoid cysts in bilateral temporal regions, and enlargement of the sylvian fissures. Glutaric aciduria type I should be included in the differential diagnosis of patients with acute encephalopathic crisis occurring shortly after poliovirus immunization. Typical magnetic resonance findings guide urinary organic acid analysis in these patients. (C) 2002 by Elsevier Science Inc. All rights reserved.