Aims White right intracardiac thrombosis (IT) is a potential cause of pulmonary embolism (PE) similar to that of stroke in left-sided IT, its prevalence and prognostic significance has not been studied in the general population. The aim of this study was to assess the age- and gender-specific prevalence of IT and its relation to PE in a population-based autopsy cohort. Methods and Results Between 1970 and 1982, 23 796 autopsies, representing 84% of all in-hospital deaths in the Malmo city population, were performed, using a standardized procedure. The relationship between IT and PE was evaluated by cohort analyses and nested case-control studies. IT was present in 1706 (7.2%) patients, 727 and 747 of whom had right and left atrial IT, respectively. PE prevalence in patients with isolated left IT, isolated right IT, and combined IT was 28.5, 35.6, and 48.9%, with RR (95% CI) of 1.5 (1.3-1.8), 2.0 (1.6-2.5), and 3.5 (2.7-4.7), respectively, compared with age- and gender-matched controls. Patients dying from ischaemic heart disease had a 3.2 (2.7-3.6) times higher risk of right IT, which was associated with 43% PE prevalence. Of all patients with PE at autopsy, right IT was found in 354 (6.5%), and the only detected source of PE in 220 (4.0%). Conclusion Right cardiac thrombosis, though difficult to assess clinically, is as common as left cardiac thrombosis and is associated with an increased risk of PE. The diagnosis should be considered in all cases of PE, especially in patients with atrial. fibrillation or myocardial infarction and in the absence of confirmed deep vein thrombosis.