One important mechanism of the regulation of membrane ion channels involves their nonfunctional isoforms generated by alternative splicing. However, knowledge of such isoforms for the members of the transient receptor potential (TRP) superfamily of ion channels remains quite limited. This study focuses on the TRPM8, which functions as a cold receptor in sensory neurons but is also expressed in tissues not exposed to ambient temperatures, as well as in cancer tissues. We report the cloning from prostate cancer cells of new short splice variants of TRPM8, termed short TRPM8α and short TRPM8β. Our results show that both variants are in a closed configuration with the C-terminal tail of the full-length TRPM8 channel, resulting in stabilization of its closed state and thus reducing both its cold sensitivity and activity. Our findings therefore uncover a new mode of regulation of the TRPM8 channel by its splice variants.