Hemoglobin A(1c) (HbA(1c)) is an indicator of long-term glycemic control. The purpose of this study was to determine whether habitual snoring is associated with increased HbA(1c) levels in non-obese and normoglycemic middle-aged men and women. A total of 6981 subjects (3362 men and 3619 women) aged 40-69 years from the Korean Health and Genome Study were examined for the study. Each participant received a comprehensive physical examination as well as a set of questions pertaining to demographic characteristics and snoring frequency. Habitual snoring was defined as a snoring frequency of > or = 4 days week(-1). After adjusting for age, abdominal obesity, and other confounding covariates, male habitual snorers showed a 1.69-fold excess [95% confidence interval (CI) 1.30-2.19] odds of having a high HbA(1c) level. Similarly, premenopausal women with habitual snoring had a 2.31 times (95% CI 1.22-4.39) significantly higher odds of having elevated HbA(1c)levels compared with non-snorers. This association was not found in postmenopausal women. Multivariate analysis revealed that male habitual snorers aged 40-50 had a 2.08-fold excess (95% CI 1.40-3.09) risk of having an elevated HbA(1c) level. In male habitual snores over 50, the strength of association was attenuated. Our findings based on cross-sectional data support a hypothesis that habitual snoring is associated with impaired glucose tolerance even in non-obese and normoglycemic men and premenopausal women. However, as waist circumference as an index of abdominal obesity (visceral adiposity) in the present study may only partially represent the effect of visceral fat, there may be a residual confounding from visceral obesity in our result. Longitudinal follow-up studies are necessary to confirm the association between sleep-disordered breathing and impaired glucose tolerance and to examine the causal relationship in a healthy population without obesity and diabetes.