OBJECTIVES: To examine the effect of implementing postcatheterization ultrasound (US) on femoral arterial thrombosis detection rates and factors associated with thrombosis in infants. BACKGROUND: Although femoral arterial thrombosis is an uncommon complication of cardiac catheterization, it can cause limb threatening complications. Previous studies assessing the utility of postprocedure US to detect thrombosis in infants have utilized US as an adjunct to standard clinical detection methods, are small scale, or include small cohorts of infants within older populations. METHODS: We reviewed institutional records of patients 0-12 months undergoing catheterization from 2007 to 2016. Demographics and procedural data were compared between the thrombosis and non-thrombosis group. Pre- and post-US groups were compared for detected thrombosis rate. Using univariate and multivariable analyses, we identified factors associated with thrombosis. RESULTS: In total, 270 patients underwent 509 catheterizations, with 40 (7.9%) documented thromboses. The rate of thrombus detection in patients younger than 6 months increased from 8.3% to 23.4% (P = 0.006) after implementing routine US. On multivariable analysis, lower weight (P < 0.001), larger arterial sheath size (P < 0.001), and longer procedure duration (P = 0.003) were independently associated with higher odds of thrombosis. CONCLUSIONS: Higher rates of femoral arterial thrombosis detection were observed since implementing an US screening program. Further studies are needed to evaluate age-related changes in hemostasis in this population and how advanced screening methods and anticoagulation protocols may help improve short-term and long-term sequelae of femoral arterial thrombosis.