Primary burning mouth syndrome (BMS) is a chronic pain of a burning quality affecting the tongue and intraoral mucosa. Currently, there are no definite diagnostic criteria; therefore, the diagnosis is made by exclusion of potential local and systemic causes that could justify the burning sensation. The etiology behind primary BMS remains unclear; however, the most acceptable theories link primary BMS with neuropathic pain. This article provides a review of primary BMS diagnosis, mechanisms, and treatment with focus on the association of BMS with pain modulation. Preliminary data are presented suggesting a link between primary BMS and a faulty inhibitory pain system. Keywords: burning mouth syndrome, pain modulation, neuropathic pain