The primary objective of this study was to examine the influence of social support on the physical activity behaviors of individual's with traumatic brain injuries. Social support was defined as a multidimensional construct that includes both type and source of social support. Different measures of social support were reviewed based on their applicability to adults with brain injuries. Based on this review the social influence scale (Chogohara, 1999) was considered the most appropriate measure for adults with brain injuries. Subsequently, a confirmatory factor analysis was conducted on data from 382 adults with with brain injuries who completed the social influence scale. Results indicated three types of positive (esteem, informational, emotional)and negative (criticism, justifying, inhibitive) support as well as three different sources of support (family, friend, caregiver). The factor structure of the measure was supported for adults with brain injuries. Results have implications for researchers working with adults with brain injuries as the social influence scale serves as a valid and reliable measure of social support within a physical activity context.