OBJECTIVE: The aim of this study was to examine the relationship between type 1 and type 2 diabetes and risk of stroke subtypes in women. RESEARCH DESIGN AND METHODS: We followed 116,316 women aged 30-55 years in 1976 through 2002 for incidence of stroke. At baseline and through biennial follow-up, women were asked about their history and treatment of diabetes and other potential risk factors for stroke. RESULTS: During 2.87 million person-years of follow-up, 3,463 incident strokes occurred. In multivariate analyses, the incidence of total stroke was fourfold higher in women with type 1 diabetes (relative risk [RR] 4.7 [95% CI 3.3-6.6]) and twofold higher among women with type 2 diabetes (1.8 [1.7-2.0]) than for nondiabetic women. The multivariate RR of ischemic stroke was increased sixfold (6.3 [4.0-9.8]) in type 1 diabetes and twofold (2.3 [2.0-2.6]) in type 2 diabetes. Risks for large-artery infarction and lacunar stroke were similar. Type 1 diabetes was also significantly associated with the risk of hemorrhagic stroke (3.8 [1.2-11.8]), but type 2 diabetes was not (1.0 [0.7-1.4]). CONCLUSIONS: Both type 1 and type 2 diabetes are associated with substantially increased risks of total and most subtypes of stroke.