To examine the association between snoring and risk of developing type II diabetes mellitus, the authors analyzed data from the Nurses' Health Study cohort. This analysis included 69,852 US female nurses aged 40-65 years without diagnosed diabetes, cardiovascular disease, or cancer at baseline in 1986. Snoring patterns were ascertained by questionnaire. During 10 years of follow-up, 1,957 women were diagnosed with type II diabetes. In analyses adjusted for age and body mass index, snoring was associated with risk of diabetes (for occasional snoring vs. nonsnoring, relative risk (RR) = 1.48 (95% confidence interval (CI): 1.29, 1.70); for regular snoring vs. nonsnoring, RR = 2.25 (95% CI: 1.91, 2.66); p for trend < 0.0001). Further adjustment for other diabetes risk factors and sleeping-related covariates only slightly attenuated the risk (for occasional snoring, RR = 1.41 (95% CI: 1.22, 1.63); for regular snoring, RR = 2.03 (95% CI: 1.71, 2.40); p for trend < 0.0001). Analyses stratified by body mass index, smoking history, or parental history of diabetes showed a consistent association between snoring and diabetes within the categories of these variables. These results suggest that snoring is independently associated with elevated risk of type II diabetes.