Extracorporeal membrane oxygenation (ECMO) is a life-saving therapy for infants and children with cardiac and respiratory failure. However, thrombosis and hemorrhage are common complications. To determine clinical and laboratory predictors of thrombosis and hemorrhage resulting from ECMO, records and slides were reviewed from 29 consecutive autopsies from 2004 through 2008 of pediatric patients who received ECMO at our institution. Laboratory results, including prothrombin time, activated partial thromboplastin time, platelet count, fibrinogen level, and activated clotting time, were analyzed, as was heparin dosing. Thrombosis and hemorrhage were very common, with 1 or both seen in 86% of patients. Sixty-nine percent had thrombosis, and 52% had hemorrhage after ECMO initiation, including intracranial hemorrhage in 33% of the patients in whom brain examination was permitted. Hemorrhage and thrombosis coexisted in 31% of patients. Thrombosis was significantly more common in patients with congenital cardiac disease. Duration of ECMO therapy, being on ECMO at death, sepsis, and patient age and sex did not predict hemorrhage or thrombosis at autopsy. Laboratory tests were poor predictors of thrombosis and hemorrhage, with no correlation between these complications and prothrombin time, partial thromboplastin time, platelet count, fibrinogen level, activated clotting time, or heparin dose. In conclusion, thrombosis and hemorrhage continue to be frequent complications among patients who die during or after ECMO therapy. Patients with congenital cardiac disease appear especially susceptible to thrombosis on ECMO. Prothrombin time, partial thromboplastin time, platelet count, fibrinogen level, activated clotting time, and heparin dose are poor predictors of thrombosis or hemorrhage for pediatric patients who die after ECMO.