Objective: To examine whether change in cognitive performance during dual task condition compared with a task in isolation, known as dual task cost, is related to fall risk of patients with multiple sclerosis.

Methods: Prospective cohort. During baseline assessment, data about balance, walking and cognitive performance of patients with multiple sclerosis were collected under a single and dual task condition. The dual task cost was calculated as a percentage of change in parameters from single to dual task conditions. Falls were recorded prospectively for six months and participants were classified as none/one time fallers and recurrent fallers (⩾2 falls). The association between dual task costs and fall status was evaluated by logistic regression. Methods: Balance research lab of university hospital. Methods: A total of 60 patients with relapsing-remitting multiple sclerosis. Methods: Not applicable. Methods: The dual task cost of the center of pressure sway area, walking velocity and correct response rate were outcome measures for balance, walking and cognitive performance, respectively.

Results: A total of 79 falls were reported by 38 of the participants who experienced one or more falls; 26 (43.3%) of them had recurrent falls. Dual tasking resulted in increased sway area and decreased walking velocity and correct response rate during walking (all p values <0.05). Logistic regressions showed that the dual task cost of the correct response rate during walking and walking velocity were associated with increased risk of recurrent falls ( P = 0.02, odds ratio = 1.34; confidence interval (CI) 1.04-3.74; P =  0.05, odds ratio = 1.23, CI = 1.02-4.45, respectively).

Conclusions: The dual task cost of cognition was related to fall, which should be considered as a target for falls evaluation and prevention strategies.