From a public health perspective, a cost-benefit analysis of using bike/pedestrian trails in Lincoln, Nebraska, to reduce health care costs associated with inactivity was conducted. Data was obtained from the city's 1998 Recreational Trails Census Report and the literature. Per capita annual cost of using the trails was 209.28 U.S. dollars (59.28 U.S. dollars construction and maintenance, 150 U.S. dollars of equipment and travel). Per capita annual direct medical benefit of using the trails was 564.41 U.S. dollars. The cost-benefit ratio was 2.94, which means that every 1 U.S. dollar investment in trails for physical activity led to 2.94 U.S. dollars in direct medical benefit. The sensitivity analyses indicated the ratios ranged from 1.65 to 13.40. Therefore, building trails is cost beneficial from a public health perspective. The most sensitive parameter affecting the cost-benefit ratios were equipment and travel costs; however, even for the highest cost, every 1 U.S. dollar investment in trails resulted in a greater return in direct medical benefit.