In this report, we describe seven new patients with a severe deficiency of glutaryl-CoA dehydrogenase in cultured skin fibroblasts. Three of the patients studied excreted high levels of glutaric acid. The remaining four patients presented a lack of significant glutaric aciduria. However, glutaric acid was found in increased levels in CSF. In both groups of patients, the urine glutaric acid levels were not related to their metabolic condition at the time of sampling. Hypocarnitinemia was a common finding. Some patients also showed defects on respiratory chain complexes in muscle biopsy. Only one patient has a normal psychomotor development. The other six patients are severely handicapped despite the attempts of different therapies. In patients with progressive neurological deterioration with dystonia and cerebellar signs associated with temporal lobe atrophy and bilateral basal ganglia damage on MRI, a glutaric aciduria type I (GA I) should always be investigated. The presence of glutaric acid in body fluids, especially in CSF, as well as plasma carnitine levels, should be determined. These procedures can lead to the diagnosis of glutaric aciduria type I.