Since November 1992, 160 patients were referred to the Vascular Surgery Laboratory for duplex scanning to assess whether a femoral artery pseudoaneurysm was present. Of these patients, 33 per cent (n = 53) had femoral artery pseudoaneurysms with maximal diameters ranging from 1.5 to 8.1 cm. Most pseudoaneurysms (79%; 42 of 53) followed diagnostic or therapeutic cardiac catheterization procedures. Pseudoaneurysms were treated by external compression using an ultrasound probe in 33 of these 53 patients, and thrombosis of the aneurysm was successfully induced in 76 per cent (n = 25) of those in whom nonoperative external compression therapy was attempted. Of the eight patients in whom compression was unsuccessful, three had severe pain that required cessation of compression, and femoral nerve involvement by the pseudoaneurysm was noted at surgery in two of the three. One additional patient refused a second attempt at compression due to discomfort. Of the other four failures of compression, four (50% overall) received anticoagulants during or prior to compression. In 25 patients with successful pseudoaneurysm thrombosis after external compression, none had severe pain from compression, and 40 per cent (n = 10) were on anticoagulants until or during compression. Four of the 53 (7.5%) pseudoaneurysms diagnosed in the vascular laboratory subsequently thrombosed spontaneously, and two patients (3.8%) experienced pseudoaneurysm rupture. Thrombosis of postcatheterization pseudoaneurysms can be achieved by nonoperative compression therapy in most patients. Severe pain during external compression suggests possible femoral nerve involvement by the pseudoaneurysm and is an indication for surgical therapy.