Background:The efficacy and safety of ultrasound-guided thrombin injection (UGTI) for the treatment of post-catheterization femoral and brachial artery pseudoaneurysms (PSA) is unclear in Japan.Methods and Results:A retrospective study of 32 consecutive patients undergoing percutaneous UGTI of post-catheterization PSA between February 2011 and February 2014 was performed. There were 23 femoral PSA and 9 brachial PSA treated with UGTI. The prevalence of CAD and smoking history were higher in the brachial PSA patients, but there were no statistically significant differences in other patient demographic factors or in the preprocedural antiplatelet therapy between the femoral and brachial PSA patients. The median dose of thrombin injected was 200 U (range, 100–600 U). The initial success rate, early recurrence rate and surgical conversion rate were 91%, 0% and 4% in the femoral PSA, and 89%, 11% and 11% in the brachial PSA, respectively. There were 2 cases of medial nerve compression in the brachial PSA group, but there were no complications in the femoral PSA group (P=0.0198). On outpatient clinical follow-up in the successfully treated patients, there were no recurrences after an average follow-up of 16 months.Conclusions:UGTI is a feasible, safe and effective less-invasive treatment for post-catheterization PSA. Brachial PSA, however, might require additional attention because of their tendency toward higher recurrence and complications. (Circ J 2015; 79: 1277–1281)