© 2019 Elsevier Inc. Background: Persons with multiple sclerosis(MS) engage in substantially more sedentary behavior than adults from the general population. Objective: Hypothesis: This preliminary, cross-sectional study examined social-cognitive theory(SCT) variables as correlates of sedentary behavior in MS. We hypothesized that scores from SCT variables for sedentary behavior change would correlate with scores from self-reported and device-measured volumes of sedentary behavior in MS. We further hypothesized that the correlations would be stronger for self-reported than device-measured sedentary behavior, and that the primary correlate of sedentary behavior would be self-efficacy. Methods: We recruited participants through a random sample of 1,000 persons enrolled in the North American Research Committee on MS registry, and 275 of the 296 persons who underwent screening volunteered for the study. Participants wore an ActiGraph accelerometer on a belt around the waist for measuring minutes per day of sedentary behavior. Participants further completed a newly-created, study-specific measure of SCT variables for reducing sedentary behavior(i.e., self-efficacy, outcome expectations, barriers, goal setting, & planning) and the abbreviated International Physical Activity Questionnaire as a self-report measure of sitting time. Results: Self-reported sedentary behavior was associated with self-efficacy(r = −0.47), goal setting(r = −0.31), planning(r = −0.35), and barriers(r = 0.39) for reducing sedentary behavior. Device-measured sedentary behavior was associated with self-efficacy(r = −0.32), goal setting(r = −0.21), planning(r = −0.18), and barriers(r = 0.20). Self-efficacy(β = −0.29), barriers(β = 0.26), and planning(β = −0.24) independently explained variance in self-reported sedentary behavior(R2 = 0.33). Only self-efficacy(β = −0.32) independently explained variance in device-measured sedentary behavior(R2 = 0.10). Conclusion: SCT constructs might be reasonable targets of a behavioral intervention for reducing sedentary behavior in MS.