This article presents the results of a special method designed for the early identification of children's and adolescents' propensity for abnormal weight gain. The basis of this technique is the principle of monitoring the actual values of body mass index for each child or young person at the age of dynamic changes in the index of the normal range. The weekly body weight of each child or adolescent who participates in the study is measured and the results are included in a special registry. Measurement of the body weight of the children and adolescents occurs in the morning at the same hour on an empty stomach after use of the toilet and performance of necessary hygiene. Afterwards, the obtained values of their body mass indices are compared with those considered normal for age, according to official data. In cases when the resulting body mass index of a child or young person exceeds the range of normal-for-age values, an in-depth medical examination of the child or adolescent is conducted together with the nature of their food intake and mode of physical activity, which may then be corrected.