Hyperlipidemia, defined as total blood cholesterol levels >240 mg/dL, has not been directly associated with an increased risk for stroke. This is different from coronary artery disease, where the relationships are clear and well understood. However recent trials show reduced stroke risk after total cholesterol reduction.

Populations at special risk
Overall, total cholesterol levels are slightly higher and HDL levels slightly lower (both patterns increase the risk of myocardial infarction) in non-Hispanic whites and Mexican Americans than in African Americans.

Relationship to pathogenesis
Concerning cerebrovascular disease specifically, what is known is that elevated total cholesterol and LDL is associated with increased degree and progression of carotid atherosclerosis, while elevated HDL levels have the opposite effect.

A little about control/treatment
To reduce the risk of both stroke and myocardial infarction, recommended levels are total cholesterol <200 mg/dL, LDL <130 mg/dL, and HDL >35 mg/dL.  This can be accomplished by diet (daily recommendation: <30% of total calories from fat, <10% of calories from saturated fat, <300 mg cholesterol), increased physical activity, and/or lipid-lowering agents. The statins (3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors) may have important effects on atherosclerotic disease in addition to their lipid-lowering properties, and recent studies show that they reduce stroke risk.