Interscalene nerve block (IS block) is the pain relief standard for shoulder surgery. But ISB is invasive and associated with complications. Infraclavicular Subomohyoid block (ISO block) may be an alternative; but evidence of comparative efficacy is sparse. We examine whether ISO block is non-inferior to IS block for pain after shoulder surgery. is to compare the efficacy of Infraclavicular Subomohyoid block (ISO block) versus Interscalene block (IS block) analgesia in shoulder arthroscopy enlightening the pros and cons of each block.This study was done at Benha university hospitals. It is a Prospective, single blind randomized clinical study which compared between infraclavicular subomohyoid block (ISO block) versus interscalene block (IS block), in outcome, the study included 90 patients udergoing elective shoulder arthroscopy, divided into three groups. The first group (group I) received general anaesthesia then infraclavicular subomohyoid block; the second group (group II) received general anaesthesia then interscalene block; the third group (group III) general anaesthesia was done. Is high significant difference between groups as regard VAS after 6, 12, 18and 24 hours after injection, also as regard pain rescue analgesia.Compared with the interscalene block, the infraclavicular subomohyoid block resulted in a significantly less frequent phrenic nerve block and overall complications and with slightly difference in postoperative analgesia.