Oral contraceptive use alone, in the absence of smoking, hypertension, or migraine, significantly increases the risk of stroke. Regardless of use or nonuse of these agents, hypertension is a risk factor for development of either thrombotic or hemorrhagic stroke. Regular cigarette smoking and a history of symptoms indicative of migraine also increase the likelihood of one or the other type of stroke, but more information is needed before a definite relationship can be established between these clinical factors and cerebrovascular disease.