Objective: To test the reliability and validity of using the Borg rating of perceived exertion (RPE) scale (ratings 6-20) in persons with multiple sclerosis (PwMS). Design: Nonrandomized repeated measures. Setting: Research laboratory. Participants: Volunteer sample (N=27) comprised of 16 PwMS (10 women) and 11 age-matched persons without multiple sclerosis (MS) (6 women). Clinical measures included symptomatic fatigue, depression, and MS functional capacity. Interventions: A submaximal cycling test was performed to estimate maximal capacity. Participants then pedaled for 2 minutes at 50% and 60% of predicted maximal oxygen consumption per unit time (Vo(2)), and physiological measures and RPE were obtained (week 1: response protocol). One week later, participants replicated the prescribed Vo2 using the RPE range from week 1 (week 2: reproduction protocol). Vo(2), heart rate, and respiratory quotient were measured continuously; RPE and workload were measured every minute; and blood lactate and mean arterial pressure were measured after exercise. Main Outcome Measures: RPE, workload, Vo2, and heart rate from week 1 to week 2. Results: PwMS had greater fatigue (P<.01) and disability (P<.001). Baseline measures were similar between groups and weeks. During exercise, RPE, workload, Vo(2), and heart rate were similar between groups. Both groups had an intraclass correlation coefficient >.86 for RPE, workload, and Vo(2). The intraclass correlation coefficient was comparatively lower for heart rate for both groups (MS group: .72, non-MS group: .83). RPE was highly correlated with Vo(2) (r=.691, P<.001) and workload (r=.700, P<.001) for the MS group. Conclusions: Results suggest that RPE can be reliably reproduced, is valid, and may be used in exercise prescription in mildly to moderately impaired PwMS during cycling exercise. (C) 2016 by the American Congress of Rehabilitation Medicine