This pilot study investigated the validity of the functional ambulatory profile (FAP) score from the GAITRite electronic pathway in persons with multiple sclerosis (PwMS) who had onset of walking impairment. Thirteen PwMS who had Expanded Disability Status Scale (EDSS) scores of 4.0-6.0 performed four trials on GAITRite™ pathway, and completed a multidimensional walking assessment including performance tests (timed 25 foot walk; T25FW, timed up and go; TUG), self reports of walking ability (Multiple Sclerosis Walking Scale-12; MSWS-12) and function (Late Life Function and Disability Inventory; LL-FDI), and free-living walking behavior (accelerometry). The FAP score correlated strongly with neurological disability (EDSS, ρ=-0.81), walking performance (T25FW, ρ=-0.82; TUG, ρ=-0.88) and self-reported walking function (LL-FDI, ρ=0.81), and moderately with self-reported walking impairment (MSWS-12, ρ=0.49) and free-living walking behavior (accelerometry, ρ=0.52). This suggests that the FAP score is a valid marker of gait impairment in PwMS who have onset of walking impairment.