Purpose: The objective of this study was to examine the hypothesis that the opioid consumption of patients who receive a rhomboid intercostal block (RIB) or a pectoral nerve (PECS) block after unilateral modified radical mastectomy (MRM) surgery is less than that of patients who receive local anesthetic infiltration., Methods: Eighty-one female patients aged 18-70 years who underwent unilateral MRM surgery with general anesthesia were randomly allocated to three groups. The first group received an RIB with 30 ml of 0.25% bupivacaine on completion of the surgery, and the second received a PECS block with the same volume and concentration of local anesthetic. In the third (control) group, local infiltration was applied to the wound site with 30 ml of 0.25% bupivacaine at the end of the surgery. The patients' total tramadol consumption, quality of recovery (QoR), postoperative pain scores, and sleep quality were evaluated in the first 24 h postoperatively., Results: Both the RIB (58.3 ± 22.8 mg) and PECS (68.3 ± 21.2 mg) groups had significantly lower tramadol consumption compared to the control group (92.5 ± 25.6 mg) (p < 0.001 and p = 0.002, respectively). Higher QoR scores were observed in the RIB and PECS groups than the control group at 6 h post-surgery. The lowest pain values were observed in the RIB group. The sleep quality of the patients in the RIB and PECS groups was better than that of the control group (p < 0.001)., Conclusion: Compared to local anesthetic infiltration, the RIB and PECS blocks applied as part of multimodal analgesia in MRM surgery reduced opioid consumption in the first 24 h and improved the quality of recovery in the early period., (© 2024. The Author(s) under exclusive licence to Japanese Society of Anesthesiologists.)