OBJECTIVE: To investigate which measures of trunk sway taken during stance and gait tasks are best correlated with Expanded Disability Status Scale (EDSS) scores of multiple sclerosis (MS) patients. METHODS: We studied 37 MS patients (mean age 43+/-10 years; 76% female; 81% relapsing-remitting MS; mean EDSS score 2.8+/-1.1). The study protocol comprised the subjective Dizziness Handicap Inventory (DHI) and recorded peak-to-peak trunk sway angles and velocities during 14 stance and gait balance tasks. 76 age- and gender-matched healthy subjects served as controls (HCs). RESULTS: Patients had significant more trunk sway than HCs (p0.4; p>0.001). Patients with normal clinical Romberg and tandem gait tests showed significantly more trunk sway than HCs when standing on one leg eyes open on foam support (p>0.001). Patients with spinal cord manifestation of MS (n=27) had higher trunk sway compared to patients without. Mean DHI score of the patients was 30+/-23.5%. DHI was highly correlated with trunk sway for all two-legged stance tasks in MS patients. CONCLUSIONS: Balance deficits in trunk sway observed in MS patients during stance and gait tasks are highly correlated with their EDSS and DHI scores, with stance and tandem gait tasks providing the highest correlations. Measures of trunk sway during stance balance tests demonstrate a MS-related functional deficit even in patients with normal clinical Romberg and tandem gait tests, and therefore have the potential to provide objective data of sub-clinical deficits.