Risk factors for systemic embolisation in patients with ventricular thrombi caused by an acute myocardial infarction were studied in 150 consecutive patients with an infarction of the anterior wall. Serial echocardiograms were performed 2-10 days after the acute event and patients were followed up for three months. Anticoagulation treatment was started only after the detection of thrombi. Of the 55 patients in whom a thrombus developed, 15 (27%) had peripheral emboli between 6-62 days; but only two (2%) of 95 patients without thrombus had emboli. Among 15 variables, the best single predictors of embolisation were age greater than 68 years (80% sensitive, 85% specific), pendulous thrombus (60%, 93%), and independent thrombus mobility (60%, 85%). Logistic regression analysis showed that a formula that included patient age, thrombus area, and the length of thrombus in the ventricular lumen predicted embolisation (sensitivity 87%, specificity 88%). There was no correlation between age and the thrombus variables. The risk of embolisation from left ventricular thrombi in acute anterior myocardial infarction can be accurately assessed from patient age and echocardiographic features. The risk of peripheral emboli is high in patients with left ventricular thrombi and those aged greater than 68.