INTRODUCTION: Somapacitan is a long-acting growth hormone (GH) derivative approved for once-weekly treatment of adult GH deficiency (AGHD). This study aimed to evaluate the efficacy and safety of somapacitan and daily GH in Japanese individuals with AGHD. METHODS: This subgroup study included the 34-week main period of the multinational, randomized, parallel-group, phase 3 trial, REAL 1 (NCT02229851). Participants received once-weekly somapacitan or daily GH (Norditropin RESULTS: In total, 36 Japanese individuals were included (18 and 18 in the somapacitan and daily GH group, respectively). 35 completed the main period (34 weeks). Mean (SD) change from baseline to week 34 in truncal fat percentage was -2.23 (2.50) %-points in the somapacitan group and -2.12 (4.21) %-points in the daily GH group. Other body composition measures also improved in both groups, including reduced visceral fat and increased lean body mass. Somapacitan was well tolerated, with a safety profile similar to daily GH. CONCLUSIONS: In Japanese treatment-naïve individuals with AGHD, once-weekly somapacitan demonstrated similar efficacy and safety to daily GH after 34 weeks of treatment. Somapacitan provides an effective alternative to daily GH in AGHD. CLINICAL TRIAL REGISTRATION: http://www.clinicaltrials.gov, identifier NCT02229851.