Background: Studies have reported the presence of sleep disorders in approximately 50-70％ of diabetic patients, and these may contribute to poor glycemic control, diabetic neuropathy, and ovight hypoglycemia.The aim of this study was to determine the frequency of sleep disorders in diabetic patients, and to investigate possible relationships between scores of these sleep disorders and obstructive sleep apnea syndrome (OSAS) and diabetic parameters (fasting blood glucose, glycated hemoglobin A1c [HbA1c], and lipid levels).Methods: We used the Berlin questionnaire (BQ) for OSAS, the Epworth Sleepiness Scale (ESS), and the Pittsburgh Sleep Quality Index (PSQI) to determine the frequency of sleep disorders and their possible relationships with fasting blood glucose, HbA1c, and lipid levels.Results: The study included 585 type 2 diabetic patients admitted to family medicine clinics between October and December 2014.Sleep, sleep quality, and sleep scores were used as the dependent variables in the analysis.The ESS scores showed that 54.40％ of patients experienced excessive daytime sleepiness, and according to the PSQI, 64.30％ experienced poor-quality sleep.The BQ results indicated that 50.20％ of patients were at high-risk of OSAS.HbA 1 c levels correlated significantly with the ESS and PSQI results (r =0.23, P ＜ 0.001 and r =0.14, P =0.001, respectively), and were significantly higher in those with high-risk of OSAS as defined by the BQ (P ＜ 0.001).These results showed that HbA 1 c levels were related to sleep disorders.Conclusions: Sleep disorders are common in diabetic patients and negatively affect the control of diabetes.Conversely, poor diabetes control is an important factor disturbing sleep quality.Addressing sleep disturbances in patients who have difficulty controlling their blood glucose has dual benefits: Preventing diabetic complications caused by sleep disturbance and improving diabetes control.