In 92 parkinsonian patients (42 men, 50 women) aged from 37-79 years (mean 62.8) the impact of cerebral atrophy as assessed by computed tomography on the course of the clinical symptomatology under levodopa during a period of 1 to 5 years was investigated. It could be shown that patients suffering from medium to severe degrees of atrophy-independent of its special location--have a less favorable response than those with normal CT findings. The data do not allow a definite decision whether cortical artrophy or ventricular enlargement are of major importance. At any rate, the width of the third ventricle seems to have no influence on the course of the clinical symptoms. After 3 years of levodopa treatment a dissociation between cerebral atrophy and therapeutic effectiveness can be observed.