The interpectoral-pectoserratus plane block is expected to anesthetize the lateral breast, but it is unclear whether the deep parasternal intercostal plane block may enhance recovery by providing analgesia to the medial breast.Patients undergoing breast cancer surgery were randomly assigned to receive either the interpectoral-pectoserratus block (single block) or interpectoral-pectoserratus combined with deep parasternal intercostal block (combined block). The primary outcome was the quality of recovery-15 questionnaire score assessed at 24 hours postoperatively. Secondary measures included dermatomal block assessment, pain severity, opioid consumption, opioid-related adverse events, hospital length of stay, and chronic postsurgical pain at 3 months after surgery.One hundred and sixteen patients were recruited, 58 in the single block group and 58 in the combined block group. There was no important difference in the 24-hour quality of recovery scores with mean (standard deviation [SD]) 123.6 (6.3) in the single block group and 123.2 (7.1) in the combined block group (mean difference, 0.4; 95% confidence interval [CI], -2.0 to 2.9; P =.731). There was greater dermatomal block on medial breast in the combined block group. There were no differences in other secondary outcomes.Addition of deep parasternal intercostal plane block was not superior to interpectoral-pectoserratus plane block alone for the quality of recovery in patients undergoing breast cancer surgery.Copyright © 2024 International Anesthesia Research Society.