Pain phenomenology in patients with fibromyalgia syndrome (FMS) shows considerable overlap with neuropathic pain. Indeed, it is increasingly recognised that patients with FMS have evidence of dysfunction of primary nociceptive and/or central pathways involved in the processing of pain relevant information. Neural dysfunction leading to symptoms of neuropathic pain can occur at the level of the spinal cord. One potential mechanism is spinal disinhibition. A biomarker of spinal disinhibition is impaired H-reflex rate dependent depression (HRDD). The current study investigated whether patients with FMS exhibit evidence of spinal disinhibition. 20 patients with FMS underwent assessment of HRDD and quantitative sensory testing. Patients with FMS had significantly impaired HRDD compared to healthy controls. Increasing impairment of HRDD was associated with increased pressure pain sensitivity. Approximately 30% of patients with FMS had levels of impairment in HRDD outside the normal range. Patients with FMS show evidence of spinal disinhibition. HRDD may provide a way of identifying patients with FMS for whom spinal disinhibition is a dominant pain mechanism.