Neurophysiologic abnormalities are frequently seen in organic acidemias, but knowledge of the specific changes in the different types of organic acidemias is lacking. We studied electroencephalogram (EEG), visual evoked potential (VEP) and brain-stem auditory evoked response (BAER) in seven children with glutaric aciduria type I (GA1) to assess the neurophysiologic features in this rare inborn error of metabolism. Age at the time of the diagnosis ranged between 3 months and 36 months. Age at the time of neurophysiologic evaluation ranged between 11 months and 36 months. At the time of neurophysiologic evaluation, severe global developmental delay was seen in four patients, dystonia in four patients, motor delay in two patients, and axial hypotonia in two patients; macrocephaly, spasticity, moderate mental retardation and borderline intelligence were each seen in one patient. One patient had autistic features characterized by lack of language and social skills, poor eye contact and stereotypical behavior. Three of seven patients showed abnormal EEG findings. Two patients showed asymmetry with intermittent occipital delta slowing in one hemisphere. This finding probably indicates underlying cerebral dysfunction, and is not a specific feature. However, it suggests that these patients may develop abnormal EEG features during the course of the disease, and thus a baseline EEG may be useful for comparison over time. One patient showed high amplitude bursts of beta in the occipital regions with left predominance while on clonazepam and baclofen. We believe this finding was due to medication effect, and that what we observed was an exaggarated response to benzodiazepine. The clinical significance of this finding is unclear. VEP and BAER were available in four patients, and we found abnormalities in three of them. Neurophysiologic evaluation may be helpful in patients with GA1 as in other types of organic acidemias to help detect subtle changes that are not reflected by neurological examination or neuroimaging studies, and it may guide future treatment plans. Detailed neurophysiologic analysis in a large series of GA1 may yield further information regarding the extent of cerebral dysfunction.