A matched case-control study was performed between 1993 and 1996 in 16 centers in the United Kingdom, Germany, France, Switzerland, and Austria. The objective was to determine the influence of oral contraceptives (OC), particularly those containing modern progestins, on the risk for ischemic stroke in women aged 16-44 years. A total of 220 women who had had an incident ischemic stroke and were compared with 775 control subjects who were unaffected by stroke. At least one hospital and one community control subject per patient was matched and interviewed with the corresponding patient for 5-year age band and for area of residence. Crude odds ratios (95% confidence intervals [CI]) for ischemic stroke were as follows. For current use of any OC versus no use 2.3 (1.7-3.2), the adjusted odds ratio (OR) 3.6 (2.4-5.4). The OC associated risk was higher for first generation than for second or third generation OC. The risk estimates for patients versus community control subjects were always lower than for hospital control subjects. No major regional difference of the risk estimates was found. Compared with nonusers of OC without hypertension, women with hypertension who used OC had an almost 10-fold increased risk. However, OC users who had had a blood pressure check before OC prescription had a lower risk than did those without such a check. Smoking > 10 cigarettes/day is associated with higher risk of stroke, particularly for OC users. No significant effect was found for duration of OC use. We conclude that although there is a small relative risk of occlusive stroke for healthy women currently using OC, the attributable risk is very small because the incidence in this age group is very low. The small increase in risk of OC use may be further reduced by preventive efforts for cardiovascular risk factors, particularly hypertension and smoking.