In multiple system atrophy (MSA) and progressive supranuclear palsy (PSP), the absence of surrogate endpoints makes clinical trials long and expensive. We aim to determine annualized whole-brain atrophy rates (a-WBAR) in idiopathic Parkinson's disease (IPD), MSA, and PSP. Ten healthy controls, 20 IPD, 12 PSP, and 8 MSA patients were studied using a volumetric MRI technique (SIENA). In controls, the a-WBAR was 0.37%+/- 0.28 (CI 95% 0.17-0.57), while in IPD a-WBAR was 0.54%+/- 0.38 (CI 95% 0.32-0.68). The IPD patients did not differ from the controls. In PSP, the a-WBAR was 1.26% + 0.51 (CI 95%: 0.95-1.58). In MSA, a-WBAR was 1.65% +/- 1.12 (CI 95%: 0.71-2.59). MSA did not differ from PSP. The a-WBAR in PSP and MSA were significantly higher than in the IPD group (p = 0.004 and p