OBJECTIVE - Morbid obesity may be accompanied by diabetes and painful diabetic neuropathy, a poorly understood condition that is manifested by mechanical or thermal allodynia and hyperalgesia. Recent studies have highlighted the importance of T-type calcium channels (T-channels) in peripheral nociception; therefore, our goal was to examine the function of these channels in the pathophysiology and development of painful diabetic neuropathy. RESEARCH DESIGN AND METHODS - In vivo testing of mechanical and thermal sensation, morphometric peripheral nerve studies, and electrophysiological and biochemical measurements were used to characterize the role of T-channels and the development of painful diabetic neuropathy in leptin-deficient (ob/ob) mice. RESULTS - We found that ob/ob mice developed significant mechanical and thermal hypersensitivity early in life that coincided with hyperglycemia and was readily reversed with insulin therapy. These disturbances were accompanied by significant biophysical and biochemical modulation of T-channels in dorsal root ganglion neurons as measured by a large increase in the amplitude of T-currents and the expression of mRNA. The most prevalent subtype, α1H (Ca v3.2), was most strongly affected. Moreover, (3β,5α, 17β)-17-hydroxyestrane-3-carbonitrile (ECN), a novel neuroactive steroid and selective T-channel antagonist, provided dose-dependent alleviation of neuropathic thermal and mechanical hypersensitivity in diabetic ob/ob mice. CONCLUSIONS - Our results indicate that pharmacological antagonism of T-channels is potentially an important novel therapeutic approach for the management of painful diabetic neuropathy.