Objectives. Noninsulin-dependent diabetes mellitus, a major risk factor for cardiovascular disease, is prevalent in more than 12 million Americans. A voluminous amount of data demonstrates that cigarette smoking is an important cause of cancer and coronary heart disease. However, the association between cigarette smoking and the risk of diabetes is virtually unexplored, especially in women. Methods. We examined the association between smoking and the incidence of noninsulin-dependent diabetes mellitus among 114 247 female nurses who were free of diabetes, cardiovascular disease, and cancer in 1976. We collected exposure information and disease status prospectively for 12 years from biennially self-administered questionnaires. Results. Current smokers had an increased risk of diabetes, and we observed a significant dose-response trend for higher risk among heavier smokers. During 1 277 589 person-years of follow-up, 2333 women were clinically diagnosed with diabetes. The relative risk of diabetes, adjusted for obesity and other risk factors, was 1.42 among women who smoked 25 or more cigarettes per day compared with nonsmokers. Conclusions. These data suggest that cigarette smoking may be an independent, modifiable risk factor for noninsulin- dependent diabetes mellitus.