Background: Persons with multiple sclerosis (MS) often experience a decrease in walking performance while simultaneously performing a cognitive task. This decrease in walking performance is termed dual task cost (DTC). Objective: To examine if mobility and cognitive function are correlates of DTC in persons with MS. Methods: Participants were 96 persons with MS who had Expanded Disability Status Scale scores that ranged between 2.0 and 6.5. To determine DTC, participants walked at a self-selected pace with and without a cognitive task while gait velocity was recorded. The effect of the cognitive task was quantified as the percent change in walking velocity between conditions. Participants further completed the timed 25-foot walk (T25FW) and Symbol Digit Modalities Test (SDMT). Centered scores for the T25FW and SDMT, and the product of the center scores, were placed into a linear regression to determine the correlates of DTC. Results: DTC averaged 12.5% (SD=9.3) and ranged between -14.1 and 42.4%. Performance on the T25FW ranged between 3.1 and 24.5s with an average of 6.8s (SD=3.1s). SDMT scores ranged between 15 and 79 with an average of 45 items (SD=12). Regression analysis revealed that age, disability, walking and cognitive performance explained 17% of the variance in DTC. The interaction between walking and cognition did not explain additional variance. Conclusions: Mobility and cognitive impairment were both independent predictors of DTC of walking in persons with MS. This raises the possibility that DTC could be reduced with modifications of either mobility or cognition.Implications for RehabilitationPersons with multiple sclerosis (MS) demonstrate a significant decrease in walking speed when engaged in a simultaneous cognitive task (e.g. dual task cost).Both walking and cognitive performance were related to dual task cost of walking in persons with MS.Improvements in walking could translate into potential improvements of dual task cost and have functional implications in persons with MS. © 2014 Informa UK Ltd All rights reserved.