The aim of the research was to evaluate the frequency of occurrence of obesity and body mass deficits among the children of grammar schools in Lublin. The research included 1,096 children (549 girls and 547 boys) at the age of 14 and 15. The measurements of height and weight of the examined children were taken and BMI - index of related to age standards presented in centile charts elaborated by the Institute of Mother and Child in Warsaw. The research showed that the average values of height, weight and BMI index of the examined children were between centile 25 and 75. Obesity features were observed with 4.9% of all the examined children (5.5% of girls and 4.4% of boys). Body mass deficits were observed with 5.5% of the examined children (6% of girls and 4.9% of boys). Incorrectness of physical development parameters are more often observed with 15-year-olds and more often in the group of girls than in that of boys. Obesity was observed with 4.9% of girls and 2.2% of boys at the age of 14 and with 6% of girls and 5.9% of boys at the age of 15. Features of body mass deficit were observed with 7.7% of girls and 5.3% of boys at the age of 14 and with 4.6% of girls and 4.4% of boys at the age of 15.