Abstract Introduction Incidentally detected masses on the leads of cardiac implantable electronic devices (CIED) present a clinical challenge, raising suspicion of infective device endocarditis. Data on the prevalence of such findings are scarce and outdated. Purpose Our aim was to determine the prevalence and evaluate predisposing clinical factors of incidental non-infectious CIED lead masses during transoesophageal echocardiography (TOE). Methods In this retrospective single-centre study, we analysed all TOE examinations performed in patients with CIED leads between January 2010 and November 2023. Patients with suspected or confirmed infectious endocarditis were excluded from this study. Patients with and without incidental non-infectious lead masses were compared regarding clinical characteristics, anticoagulation, type of CIED, and indication for TOE. Results In total, 120 patients with CIED were included. Twenty-five patients (20,8%) presented with non-infectious CIED lead masses. Laboratory findings and cardiovascular risk factors, such as arterial hypertension, dyslipidaemia, diabetes mellitus or chronic kidney disease did not differ significantly between both groups. Moreover, no association was observed between the incidence of CIED lead masses and the type of CIED implanted. Of notice, patients without therapeutic anticoagulation had significantly higher prevalence of CIED lead masses (OR 2.59, 95% CI: 1.04-6.46.; p=0.02), whereas the distribution of CHA2DS2-VASc scores did not differ significantly between both groups. Conclusion Non-infectious CIED lead masses in TOE is a frequent incidental finding. The absence of the oral anticoagulation seems to be the only clinical risk factor for such finding in our study, suggesting possible thrombogenic etiology. The high prevalence of incidental non-infectious lead masses should be kept in mind in order to avoid overdiagnosis of CIED infection and unnecessary lead extraction.