Multiple parameters for brain volume and mass were studied in 85 parkinsonian patients and in 149 normal controls aged 24 to 89 using CT scanning. In controls there was reduction in brain substance with advancing age. Increased brain atrophy in patients with Parkinson's disease (PD) was mainly observed in the younger age group of 24 to 49. This included parameters evaluating the size of the lateral and third ventricles and the size of the subarachnoid space in the frontal interhemispheric and Sylvian fissures. With computed canonical correlation analysis a formula was obtained which expressed the tendency of the atrophic process in PD to involve the areas surrounding the third ventricle and the mesial aspect of the frontal lobes more than during normal aging.