Significant hematoma formation was the sole clinical manifestation of arterial injury in eight patients among 28 with proven arterial wounds of the extremities. In these eight, normal distal pulses contributed to delayed diagnosis. Stab wounds of the canine femoral artery were created in 24 limbs. Significant hematoma formation accompanied each vessel injury. Immediate arteriography revealed no abnormality in 17 of the 24 cases. Repeat arteriography at intervals of up to 19 days showed abnormalities in limbs with previous negative arteriograms. Stab wounds of the femoral vein and thigh muscle failed to produce either significant hematomas or angiographic abnormalities. It is concluded that (1) in uncomplicated extremity wounds significant hematoma formation alone is a reliable sign of arterial injury, and that (2) arteriography may be unreliable in the evaluation of the acutely injured artery.