A prospective study of the incidence and natural history of femoral vascular complications after percutaneous transluminal coronary angioplasty. Over a 14-month period patients undergoing 144 percutaneous transluminal coronary angioplasty procedures were evaluated for the presence of complications at the femoral puncture site. After percutaneous transluminal coronary angioplasty each patient was examined by a surgeon, and then a color-flow duplex scan of the groin was obtained. On the initial scan eight pseudoaneurysms, three arteriovenous fistulas, one combined arteriovenous fistula-pseudoaneurysm, and one thrombosed superficial femoral artery were detected for a major vascular complication rate of 9%. Pseudoaneurysm formation was associated with the use of heparin after removal of the arterial sheath. Seven pseudoaneurysms (initial extravascular cavity size range 1.3 to 3.5 cm) were followed with weekly duplex scans, and all thrombosed spontaneously within 4 weeks of detection. The three patients with isolated arteriovenous fistulas were each followed for at least 8 weeks, and the arteriovenous fistulas persisted. Early surgical intervention for postcatheterization femoral pseudoaneurysms is usually unnecessary as thrombosis often occurs spontaneously. We would advocate an operative approach for pseudoaneurysms that are symptomatic, expanding, or associated with large hematomas. Iatrogenic femoral arteriovenous fistulas should be considered for elective repair, but this may be delayed for several weeks without adverse sequelae. 