OBJECTIVE : This study sought to prospectively evaluate the prevalence, risk factors, and short-term major clinical outcomes of mobile thrombus detected on transvenous leads in patients undergoing lead extraction. BACKGROUND : The prevalence and clinical significance of thrombus on transvenous leads in patients undergoing lead extraction is not well characterized. METHODS : Consecutive patients undergoing transvenous lead extraction for noninfectious indications were enrolled. Preoperative transesophageal echocardiograms were performed prospectively for all patients to examine for mobile thrombus. Anticoagulation was not started for thrombus unless other indications were present. Clinical endpoints of mortality and cardiovascular morbidity (symptomatic pulmonary embolism, myocardial infarction, or cerebrovascular accident) were assessed at a minimum of 2-month follow-up. RESULTS : A total of 108 patients underwent lead extraction for noninfectious indications. Lead thrombi were detected in 20 (18.5%) patients and all were <2 cm. Clinical and lead characteristics were not associated with formation of lead thrombi, except for younger patient age. In patients with detected thrombi, there were no short-term deaths, symptomatic pulmonary embolisms, or myocardial infarctions, except 1 patient with a stroke 3 months after lead extraction (7% vs. 5%; p = 1.00). Median follow-up was 9 months. CONCLUSIONS : Mobile thrombi on transvenous leads are commonly found in patients referred for transvenous lead extraction and are rarely associated with acute major adverse outcomes. Careful extraction of leads with small incidentally detected thrombi can likely be performed without major acute clinical sequelae. Larger studies with longer follow-up are needed to further assess the long-term clinical significance of lead thrombi.