The purpose of this study is to examine the association between sudden cardiac death (SCD) and heart rate variability (HRV) in subjects with and without type 2 diabetes and to determine whether low HRV can predict SCD in type 2 diabetes. Subjects were 8917 consecutively examined persons (3089 diabetic, and 5828 nondiabetic subjects) aged 35-69 years who underwent a 75 g oral glucose tolerance test (OGTT) together with electrocardiography (ECG). HRV was calculated from the 12-lead ECG as the coefficient of variance for 100 R-R intervals (CV(R-R)). During a median observation period of 5.2 years, SCD occurred in 56 subjects (33 diabetic, and 23 nondiabetic). Among diabetic subjects, mortality from SCD tended to be higher in subjects with a low CV(R-R) (P=0.004). After adjustment for age, gender, systolic blood pressure, total cholesterol (TC), triglycerides (TG), BMI, ischemic ECG change, and smoking history, relative risk (RR) of SCD was 2.07 (95% CI 1.02-4.17) in diabetic subjects with a CV(R-R) <2.2% compared with those with a CV(R-R) > or =2.2%. Diabetic subjects with a CV(R-R) <2.2% had significantly higher cumulative mortality from SCD than those with a CV(R-R) > or =2.2% (P=0.007). In type 2 diabetes, a low CV(R-R) carried an increased risk of SCD.