PURPOSE: To evaluate and describe the efficacy and side effects of a percutaneous thrombin injection under ultrasonography guidance for the treatment of iatrogenic pseudoaneurysms. MATERIALS AND METHODS: Eighteen consecutive iatrogenic pseudoaneurysm cases were treated with a thrombin injection. The thrombin was injected into the pseudoaneurysm cavity using a 22-gauge needle under ultrasonographic guidance. The causes of the pseudoaneurysms are as follows: post coronary angiography (9 cases), percutaneous coronary balloon angioplasty (5 cases), cerebral angiography (1 case), transhepatic chemoembolization (1 case), percutaneous transfemoral arterial stent insertion (1 case) and bone marrow aspiration for a marrow transplant (1 case). RESULTS: Only one case required a secondary thrombin injection due to recurrent flow in the pseudoaneurysm lumen, which was detected at the follow up Doppler ultrasound. Other seventeen cases were successfully treated on the first trial. There were no technical failures or complication related to the procedure. The average amount of thrombin injected was 733 IU. Nine out of 18 treated patients (50%) showed mild reactions to the thrombin including mild fever (4 cases), chilling sensation (3 cases), a chilling sensation with mild dyspnea (1 case), mild chest discomfort (1 case) after the thrombin injection. All these side effects were transient and improved several hours later. CONCLUSION: All the iatrogenic pseudoaneurysms were treated successfully with an ultrasound-guided percutaneous thrombin injection. There was a high rate of hypersensitivity to the bovine thrombin, which precaution should be taken to prevent more serious side effects.