Eighteen published trials have examined the use of neuraxial magnesium as a peri-operative adjunctive analgesic since 2002, with encouraging results. However, concurrent animal studies have reported clinical and histological evidence of neurological complications with similar weight-adjusted doses. The objectives of this quantitative systematic review were to assess both the analgesic efficacy and the safety of neuraxial magnesium. Eighteen trials comparing magnesium with placebo were identified. The time to first analgesic request increased by 11.1% after intrathecal magnesium administration (mean difference: 39.6 min; 95% CI 16.3–63.0 min; p = 0.0009), and by 72.2% after epidural administration (mean difference: 109.5 min; 95% CI 19.6–199.3 min; p = 0.02) with doses of between 50 and 100 mg. Four trials monitored for neurological complications: of the 140 patients included, only a 4-day persistent headache was recorded. Despite promising peri-operative analgesic effect, the risk of neurological complications resulting from neuraxial magnesium has not yet been adequately defined.