In 9 of 45 patients treated for dual vascular injuries of the lower extremity, concomitant fasciotomies were performed at the time of initial surgery for associated soft tissue injury, fracture, or prolonged ischemia. Eight other patients developed compartment syndrome requiring delayed fasciotomy. In seven of them, vein was either ligated or the repaired vein became occluded. In the eighth patient, peripheral venous hypertension was caused by massive swelling of the thigh. In the laboratory, compartment pressure was monitored by wick catheter in 24 hind limbs of 12 dogs subjected to experimental conditions simulating vascular injuries and their management. There was a significant increase in compartment pressure in a group that simulated arterial and venous injuries managed by arterial repair and venous outflow obstruction. Based on our study, we suggest that obstruction to venous drainage and venous hypertension are major factors in the development of compartment syndrome in dual vascular injuries of the lower extremity.