Right atrial thrombosis is an uncommon but potentially fatal disease. Due to its rarity, there is little information on its natural history, diagnosis and optimal treatment. Therefore, we reviewed all the pediatric cases with right atrial thrombi reported to Canadian Registry of Venous Thromboembolic Complications. There were 25 patients reported during the period of January 1990 to July 1995; 17 males (68%) and 8 females (32%). Their age range was 10 days to 14.6 years (median 1.8 years, mean 4.6 years). All patients had local causes of the thrombi; 21 patients had central venous lines (CVL) and the remaining 4 patients had cardiac diseases. Underlying disorders include malignancy (n=10; 40%), prematurity (n=10; 40%), cardiac diseases (n=4; 16%) and nephrotic syndrome (n=1; 4%). The presentations include suspected sepsis and fever in 11 patients (44%), asymptomatic in 9 patients diagnosed on routine echocardiogram (36%), chest pain in 3 patients (12%), malfunctioning of the CVL in 1 patient (4%) and apnea with bradycardia in 1 premature infant(4%). All patients received treatment. Twenty two patients (88%) received anticoagulation (heparin alone = 7 (28%), heparin + warfarin = 10 (40%) and warfarin alone = 5 (20%)). Eight patients (32%) received thrombolytic therapy(tPA 2 patients; streptokinase 1 patient; urokinase 5 patients). Eight patients (32%) had CVL removal (2 patients had no other treatment). Five patients (20%) had thrombectomy. There were no bleeding episodes related to treatment. Of the 23 patients that had information on the thrombi following treatment 20 patients (87%) had complete resolution of clot. Four deaths were reported. The cause of death for 2 patients were not related to thrombi and 2 autopsy reports were not available. In conclusion, right atrial thrombi are rare and occurred in patients with either CVL or cardiac diseases and majority of thrombi will resolve with treatment.