Background/aim: The aim of this study was to evaluate the effects of general anesthesia and ultrasonography-guided interscalene block on pain and oxidative stress evaluated by thiol–disulphide balance and C-reactive protein levels in patients undergoing shoulder arthroscopy. Materials and methods: A total of 42 patients aged 18–75 years who were scheduled to undergo shoulder arthroscopy were randomized into interscalene block group (Group-IB, n = 20) and general anesthesia group (Group-GA, n = 22). All patients received patient-controlled analgesia during the postoperative period. Additional analgesics were administered to patients with a visual analog scale score of > 4. Native -thiol, total -thiol, disulphide and C-reactive protein levels were measured. Patients’ visual analog scale scores, morphine and additional analgesic consumption were recorded. A shift in thiol–disulphide balance toward decreased thiol and increased disulphide levels was regarded as an indicator of oxidative stress. Results: Pain level, morphine and additional analgesic consumption were higher in Group-GA. Native-thiol and total-thiol levels were higher in Group-IB postoperatively and also disulphide levels were lower at postoperative 18 hours. C-reactive protein levels were similar in both the groups. Conclusion: Interscalene block induced less oxidative stress during the postoperative period, as evaluated by thiol–disulphide balance.