Several studies indicated the influence of age and sex on spinal alignment using spino-pelvic radiographic parameters. However, information regarding the geometrical assessment of the sagittal spinal plane in the elderly population remains limited. This study aimed to determine the apices of lumbar lordosis and thoracic kyphosis, and spinal inflection point in elderly individuals and clarify the effect of age, sex, and pelvic incidence (PI) on sagittal geometry. In total, 440 volunteers (193 men; 247 women) were enrolled. The spino-pelvic radiographic parameters were measured. The apices of thoracic kyphosis and lumbar lordosis, and the inflection point where the vertebral curvature changes from kyphosis to lordosis were investigated. We analyzed the differences in the sagittal curve shape according to the sex, age, and PI magnitude. On average, the apices of thoracic kyphosis and lumbar lordosis, and the inflection point were located at the levels of the T8/9 intervertebral disc, L3/4 disc, and L1 vertebra, respectively. Significant differences between men and women were observed with respect to the spino-pelvic parameters; however, the positions of the apices were significantly different only with respect to the lumbar apex offsets among individuals in their 70s. The inflectional point and apex of thoracic kyphosis among individuals aged >80 years were located significantly anteriorly and caudally in comparison to those among individuals aged <69 years. The apex of lumbar lordosis and the inflection point in individuals with high PI were located significantly anteriorly and cranially in comparison to those in individuals with low PI. The apices of thoracic kyphosis and lumbar lordosis, and the inflection point were located at the T8/9 intervertebral disc, L3/4 disc, and L1 vertebra, respectively. The shape of the sagittal spinal curve varied according to age and the magnitude of PI, and these findings cannot be evaluated using the conventional spino-pelvic parameters. Knowledge of standard geometrical spine shape could be useful for spinal deformity treatment in elderly patients. Copyright © 2019. Published by Elsevier B.V.