Sciatic nerve lesions occur only rarely in cardiac surgery patients. To evaluate potential causes for sciatic neuropathy, we reviewed the cardiac surgery performed at one institution during the last 15 years and found only six instances of sciatic neuropathy. We examined medical records for these six patients for potential etiologic factors and determined that four of the six patients had undergone prolonged periods of intra-aortic balloon pump therapy with a catheter placed through the femoral artery ipsilateral to the sciatic nerve lesion, and the other two patients had an ipsilateral femoral artery occlusion. In addition, four of the six patients had severe symptomatic peripheral vascular disease, and one of the other patients had severe and prolonged perioperative hypoxia. Although all these patients had pure sciatic neuropathy clinically, two of the four patients studied with electromyography had evidence of damage to the femoral nerve or quadriceps muscles ipsilaterally. In addition to the neurogenic changes, there were electromyographic findings suggestive of muscle ischemia. These results indicate that patients undergoing cardiac surgery may be at risk for development of a sciatic neuropathy if they have compromised blood flow through the femoral artery together with another cause for tissue hypoxia. Furthermore, asymptomatic ischemia of the femoral nerve or quadriceps muscles may occur in this clinical setting.