Balloon angioplasty of the superficial femoral artery was performed in 15 consecutive patients with obstructive atherosclerotic disease near the adductor hiatus. After angioplasty, extrinsic compression of the femoral artery at the adductor hiatus was shown on intravascular sonograms in five patients (33%). In retrospect, this inward deformation of the arterial wall was thought to be present in only one case before angioplasty. After angioplasty, intravascular sonography was used successfully to differentiate between residual stenosis due to residual plaque and that due to extrinsic compression of the wall of the femoral artery near the adductor hiatus. We conclude that intravascular sonography may be a useful adjunct to angiography for determining the cause of residual stenosis.