OBJECTIVE: To assess the relationship between cigarette smoking and mortality among women with type 2 diabetes in the Nurses' Health Study cohort. RESEARCH DESIGN AND METHODS: The Nurses' Health Study, a prospective cohort of U.S. female registered nurses, included 7,401 women with type 2 diabetes diagnosed at baseline or during follow-up from 1976 to 1996. Total and cause-specific mortality of these diabetic women were the outcomes of interest. RESULTS: We documented 724 deaths during 20 years of follow-up (67,420 person-years) among women with type 2 diabetes. In multivariate analyses, adjusting for age, history of high blood pressure and high cholesterol, and other cardiovascular risk factors, compared with never smokers, the RRs of mortality were 1.31 (95% CI 1.11-1.55) for past smokers, 1.43 (0.96-2.14) for current smokers of 1-14 cigarettes/day, 1.64 (1.24-2.17) for current smokers of 15-34 cigarettes/day, and 2.19 (1.32-3.65) for current smokers of > or =35 cigarettes/day (P for trend = 0.0002). Women with type 2 diabetes who had stopped smoking for > or =10 years had a mortality RR of 1.11 (0.92-1.35) compared with diabetic women who were never smokers. CONCLUSIONS: Cigarette smoking is associated in a dose-response manner with an increased mortality among women with type 2 diabetes. Furthermore, quitting smoking appears to decrease this excess risk substantially. Diabetes patients should be strongly advised against smoking.