Brachial plexus nerve blocks (BPBs) have analgesic and opioid sparing benefits for upper extremity surgery. Single-injection techniques are limited by the pharmacological duration and therapeutic index of local anaesthetics (LAs). Continuous catheter techniques, while effective can present management challenges. Off-label use of perineural dexamethasone as an LA adjuvant has been utilized to prolong single-injection techniques. The objectives of this systematic review and meta-analysis are to assess the contemporary literature and quantify the effects of dexamethasone on BPB. The authors searched for randomized, placebo-controlled trials that compared BPB performed with LA alone with that performed with LA and perineural dexamethasone. Meta-analysis was performed using a random effects model with subgroup analysis stratified by LA (long vs intermediate). The primary outcome was duration of sensory block or analgesia; the secondary outcomes were motor block duration, opioid consumption, and BPB complications. Nine trials (801 patients) were included with 393 patients receiving dexamethasone (4-10 mg). Dexamethasone prolonged the analgesic duration for long-acting LA from 730 to 1306 min [mean difference 576 min, 95% confidence interval (CI) 522-631] and for intermediate from 168 to 343 min (mean 175, 95% CI 73-277). Motor block was prolonged from 664 to 1102 min (mean 438, 95% CI 89-787). The most recent trial demonstrated equivalent prolongation with perineural or systemic administration of dexamethasone compared with placebo. Perineural administration of dexamethasone with LA prolongs BPB effects with no observed adverse events. The effects of systemic administration of dexamethasone on BPB must be investigated.