Pneumoencephalography was carried out in 23 patients with various muscular disorders, i.e. spinal neurogenic atrophy, classified as Wohlfart-Kugelberg-Welander's and Charcot-Marie-Tooth's diseases, and muscular dystrophy. EEG-registrations and psychological testing were carried out. Pneumoencephalography revealed ventricular enlargement and cortical changes in 17 out of 23 cases. Changes were found in all three groups studied; cortical changes were, however, only found in the neurogenic atrophy groups. Cases where there clearly might be exogenous causes for ventricular dilatation were excluded. The changes found, therefore, supposedly form an integral part of the disease process. It should be emphasized that the precaution does not entirely exclude a traumatic etiology in some cases. EEG-registrations (pathological in three out of 20 cases) as well as psychological evaluation (pathological in six out of 14 cases) supported the assumption of organic brain changes. Pneumoencephalography, however, seemed to be the most sensitive parameter for unveiling brain involvement in these disorders.