Thrombolytic therapy improves outcome in patients with myocardial infarction but is associated with an increased risk of intracranial haemorrhage. For some patients, this risk may outweigh the potential benefits of thrombolytic treatment. Using data from other studies, we developed a model for the assessment of an individual's risk of intracranial haemorrhage during thrombolysis. Data were available from 150 patients with documented intracranial haemorrhage and 294 matched controls. 49 patients with intracranial haemorrhage and 122 controls had been treated with streptokinase, whereas 88 cases and 148 controls had received alteplase. By multivariate analysis, four factors were identified as independent predictors of intracranial haemorrhage; age over 65 years (odds ratio 2.2 [95% Cl 1.4-3.5]), body weight below 70 kg (2.1 [1.3-3.2]), hypertension on hospital admission (2.0 [1.2-3.2]), and administration of alteplase (1.6 [1.0-2.5]). If the overall incidence of intracranial haemorrhage is assumed to be 0.75%, patients without risk factors who receive streptokinase have a 0.26% probability of intracranial haemorrhage. The risk is 0.96%, 1.32%, and 2.17% in patients with one, two, or three risk factors, respectively. We present a model for individual risk assessment that can be used easily in clinical practice.