Ashworth Scales are the most widely used tests to assess the severity of muscle spasticity. These scales offer qualitative and subjective information; consequently, there are issues concerning validity and reliability. This article presents the results of a study comparing interrater reliability of the original and of the modified Ashworth Scales for measuring muscle spasticity in elbow flexors. Fifteen patients with hemiplegia (nine men and six women) with a median age of 52 years (interquartile range, 28-64) participated in this study. Two physiotherapists rated the muscle tone of elbow flexors according to ratings criteria of the Ashworth and the modified Ashworth Scales. Kappa values for the original Ashworth and the modified Ashworth Scales were 0.17 (SE 0.21; p = 0.41) and 0.21 (SE = 0.12; p = 0.08), respectively. The scales showed similar levels of reliability (chi2= 0.0285, df=1, p = 0.7). The Ashworth Scales are not reliable for the assessment of muscle spasticity. In the absence of interrater reliability, the validity of the measurements may also be questioned.