OBJECTIVE To describe the epidemiology of cerebrovascular events in patients given or not given fibrinolytic treatment and to assess the prognostic implications and risk factors. METHODS Case series derived from the GISSI randomised trial. METHODS 176 coronary care units in Italy giving various levels of care. METHODS 5860 patients with acute myocardial infarction treated with 1.5 million units of intravenous streptokinase and 5852 patients not given fibrinolytic treatment. METHODS Cerebrovascular event, sex, age, blood pressure, history of previous infarct, site of infarction, and Killip class. RESULTS 99 of 11,712 patients (0.84%) had a cerebrovascular event. Older age, worse Killip class, and anterior location of infarction seemed to be risk factors for cerebrovascular events (40/3201 aged 65-75 v 42/7295 aged less than 65, odds ratio 2.18; 9/437 class 3 v 55/8277 class 1, 1.81; and 57/4878 anterior v 24/4013 posterior, 1.96). No significant difference was found in the rate of cerebrovascular events between patients treated with streptokinase and controls (45/5852 (0.92%) streptokinase v 54/5860 (0.77) control). More patients in the streptokinase group than in the control group had cerebrovascular events (especially haemorrhagic strokes) on day 0-1 after randomisation (27 streptokinase v 7, control), although this was balanced by late events in control patients (54 streptokinase v 45 control at one year). The mortality of patients who had a cerebrovascular event was higher than that of those who did not (47% (47/99) v 11.6% (1350/11,613]. CONCLUSIONS Although the incidence of cerebrovascular events complicating myocardial infarction was low, they increased morbidity and mortality. Treatment with streptokinase did not significantly alter the incidence, but age and poor haemodynamic state were associated with an increased risk.