PURPOSE: Diabetic cardiac neuropathy, which is characterized by reduced heart rate variability (HRV), frequently coexists with peripheral neuropathy. Gabapentin has been used for the treatment of diabetic neuropathy. We aimed to evaluate the possible effect of gabapentin treatment on autonomic function in patients with type 2 diabetes via HRV. METHODS: Thirty patients with type 2 diabetes mellitus and peripheral neuropathy and 28 age- and sex-matched healthy controls were consecutively registered. Each patient underwent HRV measurements, and diabetic patients were administered gabapentin. After 3 months of gabapentin therapy, HRV parameters were measured again. RESULTS: Baseline HRV parameters were blunted in patients with diabetes mellitus according to the controls [standard deviation of all NN intervals (SDNN, ms): 106.3+/-29.9 vs. 148.8+/-36.5, P=.001; power spectrum of the high-frequency band (HF, ms(2)): 133.6+/-98.3 to 231.4+/-197.6, P=.02; power spectrum of the low-frequency band (LF, ms(2)): 341.8+/-247.8 to 511.5+/-409.4, P=.048; LF/HF ratio: 3.3+/-2.4 to 2.6+/-1.5, P=.33]. After 3 months of treatment with gabapentin, some HRV parameters showed some improvement. SDNN (106.2+/-29.8 to 119.4 +/- 25, P=.016) and HF (133.6+/-98.3 to 167.6+/-118.3, P=.021) increased significantly. LF/HF ratio decreased (from 3.3+/-2.4 to 2.3+/-1.9, P=.039) and LF remained unchanged (341.8+/-247.8 to 352.3+/-228.9, P=.88). CONCLUSIONS: Therapeutic doses of gabapentin not only alleviate neuropathic symptoms but also improve cardiac autonomic function in diabetic patients with peripheral neuropathy.