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Purpose: The purpose of this study was to estimate the interrater reliability of the Modified Ashworth Scale (MAS) using consistent movement speeds guided by a metronome when measuring wrist flexor and ankle plantar flexor spasticity in patients with an upper motor neuron (UMN) lesion. The MAS has been found to have inconsistent interrater reliability for scoring the degree of spasticity. Method: This quantitative cross-sectional pilot study occurred in the outpatient spasticity clinic of a community rehabilitation hospital. Participants were a convenience sample of 20 patients with UMN lesions receiving botulinum toxin type A injections for focal spasticity. For each of the muscle groups tested, different pairs of evaluators scored spasticity on the MAS at a velocity of 130° per second. Evaluators were physical therapy students trained by an experienced physical therapist in MAS assessment. Weighted κ values were calculated to measure interrater reliability for each muscle group. Results: The weighted κ values for the wrist flexors and ankle plantar flexors were, respectively, moderate (κw = 0.54; 95% CI: 0.21, 0.87) and slight (κw = 0.08; 95% CI: −0.34, 0.50). Conclusion: Using consistent movement velocity, novice evaluators were able to score spasticity with reasonable interrater reliability when assessing the wrist flexors but not the ankle plantar flexors.