BACKGROUND: This study was performed to examine the status of diabetes mellitus (DM) in the community and effects of related factors on heart rate variability (HRV). METHODS: The author conducted HRV testing, a questionnaire survey, and blood chemistry analysis for fasting blood sugar (FBS) and HbA1c levels in 855 patients in a community over a period of 10 days, from August 14 to 25, 2006. The subjects were divided into a DM group and normal group by our study criteria. RESULTS: The proportion of DM was 12.6% and increased with old age. The mean measures of HRV (SDNN, Tp, Vlf, Lf, Hf, Lf/Hf) in the DM group were 22.7 (1.6) msec, 364.9 (2.7) msec2, 174.1 (3.0) msec2, 88.1 (3.2) msec2, 55.3 (3.2) msec2, and 1.6 (2.6), respectively, while those in the normal group were 32.2 (1.6) msec, 676.6 (2.8) msec2, 295.7 (3.1) msec2, 169.2 (3.4) msec2, 117.2 (3.2) msec2, and 1.4 (2.6), respectively. All parameters except for Lf/Hf were significantly lower in the DM group than in the normal group (P < 0.01). The Spearman's correlation coefficients between HRV and FBS or HbA1c were SDNN -0.222/-0.244 (P < 0.01), Tp -0.211/-0.212 (P < 0.01), Vlf -0.149/-0.132 (P < 0.01), Lf -0.188/-0.235 (P < 0.01), Hf -0.207/-0.204 (P < 0.01), and Lf/Hf (P > 0.05), respectively. CONCLUSION: This study shows that the DM group had a reduced HRV and increased pulse rate in comparison with the normal group. According to our results, the HRV test may be used accessorily for the early detection of cardiovascular autonomic neuropathy (CAN) and its related factors, as well as to prevent CAN.