Diabetes mellitus is generally accepted as an important risk factor in cerebrovascular disease. The importance of this condition varies with the type of stroke. Patients with aneurysmal subarachnoid hemorrhages (SAHs) have a lower or equivalent prevalence of diabetes mellitus than the general population. In particular, insulin-dependent diabetes is rarely present prior to aneurysmal rupture. These observations suggest that diabetic patients are not at increased risk for aneurysmal SAH.