Objectives To determine the reliability and validity of the Modified Heckmatt scale in assessing muscle echotexture in spasticity. Design Prospective, observational, 2-center study. Two residents and 2 ultrasound experienced staff physicians each rated 100 ultrasound images that were also analyzed using quantitative gray-scale. Setting Academic ambulatory spasticity clinic. Participants Participants (N=50) included 45 patients with upper or lower extremity spasticity and 5 healthy references. Interventions Not applicable. Main Outcome Measures Modified Heckmatt scale ratings and quantitative gray-scale scores. Results Inter- and intra-rater intraclass correlation coefficients were 0.76 and 0.81, respectively (P<.001), indicating good to excellent reliability. A significant relationship was found between Modified Heckmatt scores and quantitative gray-scale scores (r=0.829; P<.001). Conclusions The Modified Heckmatt scale demonstrated good reliability and validity to assess the pathologic muscle changes that occur in patients with spasticity.