The transversus abdominis plane (TAP) block has been used to relieve pain after bariatric surgery but with conflicting data on its analgesic efficacy. We conducted this systematic review and meta-analysis with trial sequential analysis to clarify whether TAP block provides effective postoperative analgesia in patients undergoing bariatric surgery. We systematically searched the literature for any trials comparing TAP block with a control group (no block or sham injection). The primary outcome was pain scores at rest (analog scale, 0-10) at 2 postoperative hours. Secondary pain-related outcomes included pain scores at rest at 12 and 24 h and both dynamic pain scores and intravenous morphine equivalent consumption at 2, 12 and 24 h. Additional secondary outcomes sought were rates of postoperative infection, haematoma, visceral injury and local anaesthetic systemic toxicity. Thirteen trials totalling 1025 patients were identified. Pain scores at rest at 2 postoperative hours were significantly lower in the TAP block group compared with the control group, with a mean (95% CI) difference of - 1.8 (- 2.5, - 1.1); I2 = 85%; p < 0.00001. All other secondary pain-related outcomes were also significantly lower in the intervention group with the exception of dynamic pain scores and intravenous morphine equivalent consumption at 2 postoperative hours. Rates of block-related complications were not significantly different between groups. The overall quality of evidence was moderate-to-low. There is moderate-to-low level evidence that the TAP block improves postoperative analgesia after bariatric surgery up to 24 postoperative hours, when compared with a control group, without major reported complications. Clinical Trial NumberPROSPERO - registration number: CRD42019136542.