Objective The purpose of this study was to examine a new MRI technology, dynamic cerebrospinal fluid (CSF) flow, to examine sporadic cerebellar ataxia patients with cortical cerebellar atrophy (CCA) and multiple system atrophy-cerebellar type (MSA-C).<br> Methods Nine CCA patients (3 men and 6 women; mean age: 64.2±6.9 years) and 31 MSA-C patients (13 men and 18 women; mean age: 62.7±6.8 years) were examined by a dynamic CSF flow analysis. All CSF flow data were evaluated by phase contrast-MRI using a 1.5T MRI scanner. The CSF flow was calculated by 15 images in the equidistant MRI sequence which was taken through a cardiac cycle.<br> Results Compared with the CCA patients, the absolute values of the mean velocity of the MSA-C patients were significantly reduced at time points 5 (CCA, 0.24±0.14 cm/s; MSA-C, 0.13±0.11 cm/s; ^* p<0.05) and 13 (CCA, -0.60±0.37 cm/s; MSA-C, -0.31±0.17 cm/s; ^** p<0.01). Significant correlations in Spearman's rank correlation coefficient were also found in MSA-C patients between the disease duration and the difference between the maximum and minimum velocities (Vheight) (r=-0.429, ^* p<0.05), the minimum velocity of the CSF (Vmin) (r=0.486, ^** p<0.01) or the length of the minor axis of the pons (r=-0.529, ^** p<0.01). The linear regressions between the disease duration and Vheight or Vmin revealed a significant strong correlation only in the MSA-C patients.<br> Conclusion The present CSF flow study showed for the first time that Vheight and Vmin revealed good correlations with the disease duration in the MSA-C patients. Furthermore, the velocity of the prepontine CSF flow tended to decrease in the MSA-C patients compared with the CCA patients, suggesting that this particular CSF flow analysis may be a new surrogate marker for differentiating both types of cerebellar ataxia.<br>