Objectives: The aim of this study was to investigate the effects of traditional interscalene block (ISB) alone and ISB combined with superior truncus block (STB)-associated diaphragm paralysis evaluated by ultrasound, duration of analgesia, and rate of complication in patients undergoing arthroscopic shoulder surgery. Patients and methods: Between January 2020 and December 2022, a total of 285 patients (158 males, 127 females; mean age: 48.0±15.1 years; range, 18 to 80 years) who underwent arthroscopic shoulder surgery under ISB, either alone or combined with STB, were retrospectively analyzed. The patients were operated under ISB alone using 30 mL 0.5% bupivacaine (n=140) or ISB using 10 mL (n=67) or 5 mL 0.5% bupivacaine (n=78) combined with STB using 20 mL 0.5% bupivacaine. Ultrasound reports of all patients’ diaphragm function were also retrieved. Duration of analgesia, need for additional analgesics, and the type of analgesic drugs, and evaluations of patient and surgeon satisfactions were evaluated. Degree of diaphragm paralysis considered as complete (≥75%), partial (25.1 to 74.9%) and no paralysis (≤25%) were evaluated for comparison between the block types. Results: The patients underwent operation due to rotator cuff rupture (n=218) or Bankart (n=67). Duration of analgesia, need for additional analgesia, and the type of analgesic drugs used were comparable between the block types. The most common complication was Horner syndrome (n=96, 33.68%) which was significantly lower in ISB (5 mL) +STB (20 mL) than the others (17.9% vs. 41.4% and 37.3%, p=0.002). The ISB (5 mL bupivacaine 0.5%) + STB (20 mL bupivacaine 0.5%) resulted in less complete diaphragm paralysis with adequate surgical anesthesia not requiring general anesthesia. Conclusion: The ISB using 5 mL of 0.5% bupivacaine + STB instead of traditional ISB alone can be preferred due to the low rate of complete hemi-diaphragm paralysis with adequate surgical anesthesia/analgesia and high patient and surgeon satisfaction.