BACKGROUND: Efforts to increase community levels of physical activity through the development of multiuse urban trails could be strengthened by information about factors predicting trail use. This study examined whether reasons for trail use predict levels of physical activity on urban trails. METHODS: Adults (N = 335) living within a 1-mile buffer zone of urban trails in Chicago, Dallas, and Los Angeles completed a self-report measure assessing demographics, reason for trail use, and physical activity on the trail. Accelerometers measured total daily moderate-to-vigorous physical activity (MVPA). Environmental features of the urban trail were assessed with the Systematic Pedestrian and Cyclist Environmental Scan for trails measure. Multivariate regression analyses were conducted that accounted for clustering of individuals within trail segments. RESULTS: After controlling for demographic and environmental factors and total daily MVPA, reasons for trail use significantly predicted recreational but not transportation activity. Recreational trail activity was greater for participants who reported exercise and health reasons for trail use as compared with other reasons (ie, social interaction, enjoying nature, walking pets) for recreational trail use. CONCLUSIONS: To increase the use of urban trails, it may be useful to promote the health and exercise benefits of recreational trail use.