Introduction Adolescent idiopathic scoliosis (AIS) surgery aims to obtain a flexible and stable spine, correct axial rotation and halt curve progression by fusing the least number of motion segments. Longer fusions can improve deformity correction, but late decompensation and lumbar degeneration may occur. Even some daily issues can be problematic in some scoliosis patients. Reduction in mobility, segmental mobility adjacent to fusion, degeneration of junctional unfused levels and low-back pain (LBP) results in poor outcomes. It is reported that AIS patients have more mental and psychological problems including depression. Preoperative concerns due to deformity may continue postoperatively as instrumentation fuses motion segments. We wanted to present the relationship between the remaining mobile segments and Scoliosis Research Society-22r (SRS-22r) mental health (MH) scores of AIS patients. Methods It is a retrospective study of 110 posterior fusion AIS patients, age between 10 and 18 years, and followed-up for at least two years who filled SRS-22r forms both preoperatively and in postoperative second year (POY2). Patients are grouped according to the lowest instrumented vertebra (LIV) as LIV L5: group 1, LIV L4: group 2, LIV L3 and above: group 3. Results A statistically significant difference (SSD) was not found in preoperative and POY2 comparison of truncal shift (TTS), thoracic kyphosis (TK), lumbar lordosis (LL), sagittal balance (SB) in group 1; SB in group 2, and LL in group 3 (p>0.05). SSD was found in all other radiologic measurements of groups and in all patients. No SSD was found in function and MH in group 1, in function and pain in group 2 and in pain in group 3 and all patients (p>0.05). SSD was found in the remaining SRS-22r subscales. There was an SSD between groups 1 and 2 in terms of instrumentation level (p=0.013). SSD was found between groups 1 and 2 in preoperative Cobb angle (p=0.016). SSD was found between groups 2 and 3 in POY2 Cobb angle (p=0.025). SSD was found between groups 2 and 3 in POY2 apical vertebral translation (p=0.01). There was no SSD in other radiological parameters (p>0.05). SSD was found between groups 1 and 2 (p=0.02) and between groups 1 and 3 (p=0.037) in terms of POY2 MH, but no SSD was found between groups 2 and 3 (p>0,05). There was no SSD in other preoperative or POY2 SRS-22r subscales (p>0.05). Conclusion More distal LIV is associated with a reduction of mobility and SRS scores. The self-image scores of groups were not statistically different. However, in group 1, MH was significantly lower. With the improvement of body images, patients start to worry about mobility instead of cosmesis. Higher depression has been reported in AIS patients. In POY2, there was no SSD between groups in terms of pain, function and satisfaction in addition to the self-image score as indicated in the literature. We especially recommend that L5 LIV patients should receive psychiatric support in order to prevent anxiety, and inform and support them that they are not different in terms of pain, self-image and function scores compared to more proximal LIV patients, and also we recommend encouraging L5 LIV patients that POY2 SRS22-r pain, self-image, satisfaction, subtotal and total scores are improved. As reported in the literature which shows increased suicidal thoughts and depression in scoliosis patients; our findings regarding MH are important and considerable.