Physical inactivity is a major health problem in the United States, particularly in elderly and disabled populations. Little research exists examining the relationships between aspects of the built environment and physical activity in older adults and individuals with multiple sclerosis (MS). We adopted a social cognitive perspective to examine the independent roles of perceptions of the environmental, self-efficacy and functional limitations in understanding physical activity levels among elderly women and women with MS. Older women (n=136) and women diagnosed with MS (n=173) were recruited to participate in separate cross-sectional studies. Individuals completed a battery of questionnaires and wore an activity monitor for 7 days. All measures were issued and collected through the mail with the use of self-addressed, pre-paid envelopes. Initial correlational analyses indicated that self-efficacy, functional limitations and environmental perceptions were significantly related to physical activity. Among older women, self-efficacy, functional limitations and street connectivity demonstrated independent contributions to physical activity behavior. Only self-efficacy and functional limitations demonstrated significant associations among women with MS. The prospective contributions of the environment and individual factors to changes in physical activity need to be determined.