Hey HWD, Ramos MRD, Lau ETC, et al. - A cross-sectional study on a randomly selected prospective cohort of patients presenting to a single tertiary spine center was conducted to present the clinical and radiographic parameters of patients with S- and C-shaped thoracolumbar sagittal spinal profiles, and to identify predictors of these profiles in a natural, relaxed sitting posture. In the analysis, 54.2% had S-shaped curves when sitting out of the 120 patients included, The results of this study demonstrate that stiffer lumbar curves (eg, patients with degenerative spondylolisthesis and degenerative scoliosis) or those who have a predilection for an S-shaped standing sagittal profile when sitting (eg, high PI) may be more amenable to fusion in accordance with previously studied sagittal realignment targets. For prevention of potential junctional failures, more flexible curves may benefit from less aggressive lordotic realignment.