In multiple system atrophy (MSA), symptoms associated with dysfunctions of the brainstem and autonomic nervous system are important prognostic factors. We investigated brainstem involvement in 12 patients with MSA with predominant cerebellar symptoms (MSA-C) (mean age, 56.3 +/- 9.9 years, median disease duration, 3 years), and 11 controls (57.6 +/- 12.0 years) matched for age using diffusion-weighted MR imaging (DWI). We demonstrated that apparent diffusion coefficients (ADCs) in the pons and middle cerebellar peduncle of MSA-C patients are significantly higher than those of normal controls even though the patients are in the early stage of the disease. Furthermore, we demonstrated that increased ADC values correlated well with the disease duration. The current study demonstrated that DWI is a useful noninvasive method for the quantitative evaluation of the brainstem involvement in MSA-C patients.