We studied the relationship between the Brunnstrom stages obtained after rehabilitations and Wallerian degenerations detected by magnetic resonance imaging (MRI). Forty-nine hemiplegic patients were retrospectively studied. The patients were grouped into a low stage group (30 patients) demonstrating Brunnstrom stages I approximately IV and a high stage group (19 patients) demonstrating stages V approximately VI. MRI detected Wallerian degenerations as changes of signal intensity in corticospinal tracts on T2-weighted images. The signals were hypointense or hyperintense compared to the normal side according to the intervals between the MRI examinations and the ictuses. MRI showed Wallerian degenerations in 27 of 30 patients in the low stage group and 5 of 19 patients in the high stage group. The difference between the two groups was significant (p less than 0.005).