Aim:This study aimed to investigate the importance of thoracic kyphosis (TK) for treatment preference in patients with Lenke Type 5C adolescent idiopathic scoliosis by comparing radiological outcomes of the patients who underwent selective fusion (SF) or nonselective fusion (NSF).Material and Methods:Twenty-nine patients with Lenke Type 5C AIS were included and then divided into two groups as per the fusion procedure used in the surgical treatment. SF group including 16 patients (14 female patients; mean age = 15.56 yr; age range, 14−18) with normal TK and NSF group including 13 patients (nine female patients; mean age = 15.54 yr, age range, 13−18) with thoracic hyperkyphosis. Thoracolumbar/lumbar (TL/L) Cobb, thoracic (T) Cobb, TK and lumbar lordosis (LL), pelvic incidence (PI), pelvic tilt (PT), and sacral slope (SS) were measured on standing spine radiographs preoperatively and at the final follow-up. The correction rates (CRs) of Cobb angles and the difference in each other radiological parameters were calculated.Results:No significant differences were observed in the mean CRs of T/L Cobb and T Cobb angles, PI, SS, and PT (p = 0.313, p = 0.444, p = 0.51, p = 0.472, and p = 0.14, respectively). However, significant differences were observed in the mean TK angle, which was −2.13° ± 13.52° (range, 29–27°) in SF group and 28.46° ± 15.05° (range, −4°–°47°) in NSF group (p = 0.001), and LL angle was 0.88° ± 14.23° (range, −21°–32°) in SF group and 11.54° ± 17.79° (range, −31°–34°) in NSF group (p = 0.016).Conclusion:In patients in whom Lenke\'s sagittal modifier is N, SF can be performed efficiently. NSF can be preferred for those with (+) Lenke\'s sagittal modifiers as it provides better TK control.