The Modified Ashworth Scale (MAS) is currently a widely used clinical scale to evaluate muscle spasticity. However, it lacks reliability and the validity, of the MAS as a clinical measure of muscle spasticity has been challenged. The aim of the present study was to examine the validity of the MAS in patients with wrist flexor spasticity after stroke by using the Hslope/Mslope (Hslp/Mslp) ratio as the new index of alpha motoneuron excitability. Twenty-seven adult patients (14 women and 13 men) with first ever stroke resulting in hemiplegia with a mean (SD, range) age of 57.9 (11.6, 37-75) were included in the study. The main outcome measures were the MAS for the clinical assessment of spasticity, and the Hslp/Mslp for the neurophysiological evaluation. There was not a significant correlation between the MAS scores and Hslp/Mslp ratio (r = 0.38, p > 0.05). The mean of the Hslp/Mslp did not show a hierarchical increase with the MAS scores. The findings indicate that the MAS is not a valid and ordinal level measure of muscle spasticity.