Since vein grafting is often required during transplantation of free muscle flaps but is associated with a higher failure rate than those flaps transplanted with primary anastomoses, we sought to compare primary repair with the use of vein grafting in an experimental setting. We transplanted the gracilis muscle to the contralateral side in 98 rats using four different methods of vessel repair. In the Control group (n = 28), both femoral vessels were anastomosed primarily. In Experimental Group 1 (n = 25), the femoral artery was anastomosed with an epigastric vein graft and the femoral vein was anastomosed primarily. In Experimental Group 2 (n = 25), the femoral vein was anastomosed with a femoral vein graft and the femoral artery was anastomosed primarily. In Experimental Group 3 (n = 20), both femoral vessels were anastomosed with vein grafts. The Control and Experimental Groups 1-3 survival rates were 89.3, 76.0, 84.0, and 70.0%, respectively; none of the experimental group survival rates was significantly different from that of the control (P < 0.5). This study demonstrates that the use of size-matched, interpositional vein grafts in the arterial or venous pedicle of the rat gracilis muscle flap during transplantation did not significantly decrease flap survival as compared to primary arterial or venous anastomoses. If the observed failure rate persisted with expansion of the study groups to 60-100 animals each, the failure rate of flaps with vein grafts would be significantly lower and comparable to failure rates reported in some clinical series. The large numbers necessary to significantly show this decrease make this model impractical for further studies.