BACKGROUND AND PURPOSE: Paralysing lumbar disc herniation (LDH): what and when to do? Few studies have analyzed the optimal timing of surgery in case of paralysing LDH. METHODS: Twenty-four charts were retrospectively reviewed of patients suffering of LDH with severe motor deficit. RESULTS: There were 16 men and eight women. Mean age was 45.1 years. Seventeen patients suffered of lumbar pain, 15 of radicular pain and all of a severe motor deficit, implying mostly the ankle flexion (17 patients). LDH was most frequently located at L4/L5 or L5/S1 level. Surgery was proposed to all patients at the end of the consultation. Nine patients were operated within 48 hours. The mean interval between onset of motor deficit and operation was 20 days. The statistical analysis did not reveal any significant difference among different prognostic factors between the 17 patients with good motor recovery and the seven patients with poor motor recovery. In particular the operative delay did not appear to influence the degree of motor recovery. Literature review on paralysing LDH provides five published series since 1996, including 28 to 116 patients. Two series, including the single prospective one, conclude that the degree of recovery of motor function is inversely related to the degree and duration of motor deficit. CONCLUSIONS: Our retrospective series of 24 operated paralysing LDH did not reveal any prognostic factor for motor recovery. There is no evidence based medicine data in the literature about the optimal timing of decompressive surgery. A relative consensus exists among spine surgeons for paralysing LDH: since operative indication is obvious, surgery should be done as soon as possible.