Our previous research indicated that an Internet intervention was effective in increasing self-reported physical activity in persons with multiple sclerosis (MS). The present study examined the efficacy of the same Internet intervention in persons with MS by using both objective and self-report measures of physical activity. Participants (N = 21) wore an accelerometer around the waist for 7 days and then completed the International Physical Activity Questionnaire (IPAQ) and Godin Leisure-Time Exercise Questionnaire (GLTEQ) before and after receiving the 12-week Internet intervention. The Internet intervention resulted in moderate increases in accelerometer activity counts (d = 0.68) and steps counts (d = 0.60), and this was paralleled by small increases in IPAQ (d = 0.43) and GLTEQ (d = 0.34) scores. The number of weeks that persons logged on was correlated with change in accelerometer activity counts (r = 0.42) and step counts (r = 0.37) but not change in IPAQ (r = 0.10) or GLTEQ (r = 0.08) scores. The novel contribution of this study was the observation that an Internet intervention was efficacious for increasing physical activity in persons with MS by using both objective and self-report measures.