Introduction. The possibility of detecting postural defects early, a significant development with respect to available therapeutic methods, and an awareness of the necessity for continuous and individually adjusted treatment, are regarded as an important progression in the modern conservative treatment of faulty postures. Aim. This work aimed at determining changes in body postures in 10- and 13-year old children within a 3-year period. Materials and methods. This research was conducted in Mława in two primary schools and involved 10-year old children, who were reexamined after a 3-year period, at the age of 13. The final group included in this research consisted of 76 subjects. Results and Discussion. Changes in body posture observed in the study group over the 3-year period are as follows: 34.29% of children manifested excellent and good posture during examination I; whereas during examination II 45.71% of children had good posture. The adopted methodology did not allow us to determine physiological changes concerning body silhouette. However, it allowed us to detect posture abnormalities, and to diagnose postural defects. Conclusions. The results confirmed the occurrence of changes in body postures in children between the 10th and 13th years of age. These changes, defined as detected body posture abnormalities, showed both improving and worsening tendencies with respect to the analyzed elements of body posture. A general percentage analysis showed an improvement in the body posture of children within a 3-year period.