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Aim Ultrasound-guided transversus abdominis plane and rectus sheath block (TAPRSB) decreases pain scores and narcotic use postoperatively after colorectal surgery (CRS). It is unclear if the effectiveness of TAPRSB varies according to whether it is performed preoperatively or postoperatively. Our aim was to investigate this.Method We compared patients who underwent preoperative TAPRSB or postoperative TAPRSB during minimally invasive CRS. Primary end-points were pain scores and oral morphine milligram equivalent (MME) use postoperatively. Secondary end-points included perioperative factors affecting pain scores and postoperative MME. Summary statistics and univariate analysis by nonparametric tests were utilized. The mixed-effect model was applied to model the repeatedly measured pain score.Results From April 2015 until May 2018 168 patients received TAPRSB before (115) or after (53) minimally invasive CRS. The cohort included 79 (47.0%) women, and had an average age of 59.11 (AE12.32) years and mean body mass index of 28.32 (AE5.82) kg/m 2 . Indication for surgery was cancer in 66 (39.3%), polyp in 43 (25.6%) and diverticulitis in 43 (25.6%). Right colec-tomy was performed in 61 (36.3%), low anterior resection in 46 (27.4%) and sigmoid colectomy in 40 (23.8%) patients. The demographics of the groups were similar. Postoperative TAPRSB was only associated with lower pain scores at 12 h postoperatively. As secondary outcomes, average pain scores and MME were lower in patients who were older, had right colectomy or intracorporeal anastomosis.Conclusions Postoperative TAPRSB resulted in lower pain scores than preoperative TAPRSB 12 h after minimally invasive CRS, but otherwise no differences were seen in pain scores or MME use.Keywords Transversus abdominis block, rectus sheath block, milligram morphine equivalent, pain score, minimally invasive colorectal surgeryWhat does this study add to the literature? This study provides data regarding the timing of transversus abdominis plane and rectus sheath block and its effect on postoperative pain scores and narcotic use in patients undergoing minimally invasive colorectal surgery. It also offers more data regarding a specific type of block, which includes four injection sites.Comparison of preoperative vs postoperative transversus abdominis plane J. Xia et al.