Some secondary complications of multiple sclerosis (MS) can be countered by physical activity (PA) participation. To encourage PA participation, practitioners may deliver risk information about secondary complications of MS proceeded by messages encouraging PA participation. This study examined the effects of risk information (or no risk information) followed by gain- or loss-framed messages on perceived risk of secondary complications, fear arousal, and PA intentions, behaviour, and self-efficacy in people with MS. Two-hundred sixty-two participants (M age = 41.62, SD = 9.47) completed measures on Day 1, Days 2-5, and Days 6, 14, and 28. Participants read corresponding risk information and/or framed PA messages on Days 2-5 (one health topic per day), covering health topics relevant to people with MS (i.e., chronic diseases, falls, fatigue, and mental health). Repeated measures ANCOVAs showed risk information participants had higher scores than no risk information participants for PA and perceived risk (ps < .04). ANCOVAs revealed that participants who read information about chronic diseases had higher scores for intentions than participants who did not read risk information (p = .04). Participants who received risk information/gain-framed messages had higher fear arousal regarding chronic diseases, falls, and mental health compared to no risk information/gain-framed participants (ps < .02) and higher fear arousal regarding fatigue compared to no risk information/gain-framed (p < .001) and risk information/loss-framed (p = .002) participants. In summary, the results suggest the provision of risk informationâ€”and in some instances gain-framed messagesâ€”effectively changes PA and potential antecedents in people with MS.