Our objective was to determine the efficacy of ultrasound-guided direct injection of human thrombin to close postcatheterization pseudoaneurysms and to evaluate the midterm results of this new percutaneous technique by ultrasound follow-up. One hundred one postcatheterization pseudoaneurysms in 100 patients were treated by direct injection of human thrombin (mean dose 200 IU, range 50-750 IU) under ultrasound guidance. Patient demographics, clinical data and ultrasonographic morphology of the pseudoaneurysms were analyzed. Midterm (mean 99 days, range 25-210 days) ultrasonographic follow-up was performed in 57 of 82 called patients (69.5%). Ninety-six of 101 pseudoaneurysms thrombosed completely after the first procedure. Of the remaining 5 pseudoaneurysms, 3 were treated successfully after the second attempt, and 2 patients underwent surgical repair; thus, the primary success rate was 95% (96 of 101), and the overall success rate was 98% (99 of 101). No changes in distal pulses or other adverse events were noted immediately or 1 day after the procedure. Ultrasound follow-up revealed complete disappearance of the pseudoaneurysm in 70% (40 of 57), presence of small, residual groin hematoma in 26% (15 of 57), and partial reperfusion of the pseudoaneurysm in 3.5% (2 of 57). Human thrombin injection under ultrasound guidance is a very effective and safe method of therapy. Failure (immediate and late) of the technique as well as procedure-related complications are very rare. In our institution, sonographically guided human thrombin injection has become the treatment of choice for postcatheterization pseudoaneurysms.