This study was aimed at evaluating of the antero-posterior spinal curvatures in the sagittal plane, in subjects in the 2nd stage of ontogenetic development. The examination covered 192 children from the 6th grade of primary school and 1st grade of secondary school in Strzelce Opolskie. The mean age of subjects was 12.8 ± 0.8 years. All of the children were divided into two subgroups with regard to sexual maturity. The division was based on evaluation of biological development of subjects (occurrence of secondary sexual characteristics). Body posture was evaluated by means of the photogrammetric method using projection moire. A significant gender dimorphism was observed in the analyzed angular parameters. Girls with explicit secondary sexual characteristics showed significantly higher angular values for particular sections of the spine and the total value of all parameters was also higher than in comparison to boys at the same stage of biological development.