Muscle dysmorphia has recently been described as a variant of body dysmorphic disorder that involves an intense preoccupation with one's perceived lack of muscle size. Currently, no assessment measures specific to the cognitive, affective, and behavioral dimensions of the construct of muscle dysmorphia have been published. To address this need, the authors developed the Muscle Appearance Satisfaction Scale (MASS), a brief 19-item self-report measure for the assessment of muscle dysmorphia symptoms. Psychometric evaluation of the MASS across two samples of male weight lifting participants (total N = 372) revealed a stable five-factor structure. An evaluation of factor content resulted in the following factor labels: Bodybuilding Dependence, Muscle Checking, Substance Use, Injury, and Muscle Satisfaction. Internal consistency, test-retest reliability, and construct validity were established with the MASS total score and its subscales. The authors believe the MASS will be a useful measure for research and applied work relating to muscle dysmorphia.