An infant presented at three weeks of age with a rapidly enlarging head and hypertonicity. The diagnosis of glutaric aciduria type I (GAI) was confirmed by the absence of the enzyme glutaryl-CoA dehydrogenase in fibroblast culture. A CT scan at that time showed diffuse attenuation of cerebral white-matter. Scans at five and 10 months of age showed loss of white-matter volume and diffuse cerebral atrophy, most prominent in the frontal and temporal regions. GAI should be considered in the differential diagnosis of infants and children with neurological dysfunction who have CT-scan findings of white-matter attenuation and/or cerebral atrophy, most prominent in the frontal and temporal regions, and/or changes in the basal ganglia or thalamus.