While behavioral, demographic and vocational factors are commonly know as risk factors for sustaining a traumatic injury, less is known about the social, demographic and economic determinants of outcome following injury. The Lower Extremity Assessment Project (LEAP) identified a prospective cohort of 601 patients who were admitted to eight level I trauma centers in the United States for treatment of severe lower extremity trauma. Prospective data was accumulated on these individuals throughout their initial hospitalization and at regular follow-up intervals including a cohort at seven years post-injury. The results of the LEAP investigations showed that even at five to seven years following injury, reconstruction for the treatment of injuries to the lower extremity typically result in functional outcomes equivalent to those of the amputation. Clearly, factors other than the traditional variables such as fracture healing, joint function, and ability to ambulate have a profound effect on the patient's estimation of improvement. The purpose of this report is to summarize the data from the LEAP study and other investigations related to demographic, social and behavioral factors which impact outcome following lower extremity injury.