Two siblings presented with macrocephaly, psychomotor delay, and progressive dystonia. The initial diagnosis was of hydrocephalus and bilateral temporal cerebrospinal fluid collections. Following ventriculoperitoneal shunting, the patients showed only modest neurological improvement. Metabolic investigations performed later in the course of the disease disclosed increased levels of glutaric acid in the urine and decreased levels of serum carnitine, which were confirmatory of glutaric aciduria type 1. The association of macrocephaly, dystonia, and bilateral temporal arachnoid cysts, shown either by computed tomography or magnetic resonance imaging, seems to be diagnostic of glutaric aciduria type 1. The authors report these two cases as they think they might be of interest to neurosurgeons.