BACKGROUND--The major risk factors for stroke are well described and there is good evidence that the risks associated with hypertension and cigarette smoking are reversible by appropriate interventions. However, if disease prevention measures are to be efficient, it is important that a system which can identify individuals at high risk of stroke be available for use in general practice. AIM--A study was therefore undertaken to design an effective and practical system for detecting men aged 40 to 59 years at high risk of stroke in primary care. METHOD--Stroke incidence and risk factor data were examined in a cohort of 7735 men aged 40 to 59 years who had taken part in the British regional heart study. Analysis was performed using data from initial entry into the study and then from five and 11.5 years of follow up. Subjects were randomly selected from the age-sex register of one general practice in each of 24 different towns throughout the United Kingdom, representing the full range of cardiovascular mortality rates. RESULTS--A simple scoring system derived from logistic regression using age, systolic blood pressure, current cigarette consumption, and evidence of anginal chest pain was able to detect more than 80% of all strokes occurring within five years in the top fifth of the score distribution. The inclusion of other risk factors for stroke did not increase the score's predictive ability. The combination of smoking and hypertension, while much less sensitive than the scoring system, was a better indicator of risk than any single risk factor, all of whose predictive values were poor. CONCLUSION--Based on readily measured variables, this scoring system could be used in general practice to identify men at high risk of stroke who would benefit from further intervention. Effective identification of high risk individuals requires assessment of the combined effects of multiple risk factors.