Introduction Understanding the impact of scoliosis surgery on lung function is important for counseling patients about risks and benefits of surgery. We prospectively compared the trends in lung function test (LFT) results prior to and after scoliosis surgery in children with neuromuscular diseases, or dysmorphic syndromes. We hypothesized a stabilization. Methods We prospectively included children with neuromuscular or syndromic scoliosis able to perform LFTs. We studied (Forced) Vital Capacity ((F)VC), the ratio of Forced Expiratory Volume in 1 second (FEV1) and FVC, and Peak Expiratory Flow (PEF). Preoperative LFT results were compared with results 3-4 months after surgery. The mean monthly change in LFT results up to 2 years after surgery was compared with the preoperative natural history using linear mixed effects models. Results We included 43 patients. No significant change was observed in absolute values of (F)VC, FEV1/FVC and PEF prior to and after surgery. Median standardized VC, FVC and PEF decreased significantly after surgery from 59 to 58%, 60 to 51% and 61 to 53% respectively. The monthly rate of change in FVC was -0.13 % (95% CI -0.42 to 0.17) prior to surgery and -0.20% (95% CI -0.42 to 0.03) after surgery, mean difference -0.07 (95% CI -0.46 to 0.31; p=0.36). Conclusion No stabilization of lung function 3-4 months after scoliosis surgery was observed in children with neuromuscular and syndromic scoliosis with restrictive lung function disease. The effect of surgery on the rate of lung function decline remains inconclusive.