Blood glucose levels of 220 days were recorded in 85 type 2 diabetic patients for monitoring glycemia for 48-72 h each one by the continuous glucose monitoring system (CGMS). Frequencies of nocturnal hypoglycemia (blood glucose≤2. 8mmol/L) were estimated when bedtime blood glucose levels were≤4.4mmol/ L,≤5.0mmol/L,≤5. 6mmol/L,≤6.1mmol/L,≤6. 7mmol/L, or≤7. 2mmol/L respectively. Nocturnal hypoglycemia occurred in 39 nights of 220 days (17.7%) of 26 patients and their bedtime blood glucose level was (4.4?2.6)mmol/L with a range from 2. 2 to 12. 6 mmol/L. Using a cut-off of bedtime blood glucose at≤6. 7 mmol/L, area under the ROC curve was reached maximal value (0. 359?0. 046). The positive predictive value was 25% and the negative predictive value was 91. 7%. CCMS is a useful tool to detect unaware nocturnal hypoglycemia.