Background: Metabolic comorbidity is overrepresented in people with multiple sclerosis (MS) and is associated with adverse MS outcomes. Excess visceral adiposity, approximated using waist circumference (WC), is a risk factor for metabolic comorbidity and predicts poorer outcomes in other neurologic diseases. Objective: To evaluate the association between WC and clinical and disease characteristics in people with MS. Methods: North American Research Committee on MS (NARCOMS) registry participants reported height and weight (used to calculate body mass index (BMI)) and were mailed a tape measure with instructions to measure WC. We considered WC continuously and used cut-points derived from the abdominal obesity criteria for the metabolic syndrome (men: WC ⩾ 40 in; women: WC ⩾ 35 in). We assessed the association between WC and disability (Patient-Determined Disease Steps) and symptom severity (validated scales) using multivariable-adjusted multinomial models. Results: Of 6367 responders with MS, we included 5832 (92%). Of these, 3181 (55%) reported WC meeting criteria for the abdominal obesity component of metabolic syndrome. In multivariable models adjusting for overall obesity status, WC was associated with 47% increased odds of severe versus mild disability (odds ratio (OR): 1.47; 95% confidence interval (CI): 1.22–1.78). Conclusions: Increased WC is associated with more severe disability, even after adjusting for overall obesity in this large cross-sectional survey.