The cross-sectional relation of self-reported usual sleep time to diabetes mellitus (DM) and impaired glucose tolerance (IGT) was assessed in 1486 adult participants in the Sleep Heart Health Study. Median sleep time was 7 hours per night, with 27% of subjects sleeping 6 hours per night or less. Compared with those sleeping 7 to 8 hours per night, subjects sleeping 5 hours per night or less and 6 hours per night had adjusted odds ratios for DM of 2.51 and 1.66, respectively, after adjustment for age, sex, race, body habitus, and apnea-hypopnea index. Adjusted odds ratios for IGT were 1.33 and 1.58, respectively. Subjects sleeping 9 hours per night or more also had increased odds ratios for DM and IGT. These associations persisted when subjects with insomnia symptoms were excluded, suggesting that voluntary sleep restriction may contribute to the large public health burden of diabetes.