Nowadays, the importance of physical activity is emphasized and numerous studies confirm the importance of its role in achieving and maintaining health. The role of physical activity is significant in all phases of life, and it is particularly crucial at an earlier age, childhood and adolescence, since it is an essential precondition for development. Although the direct link between physical activity and health has long been known and proven, one of the major problems of modern man is its lack. Modern society is dominated by a sedentary lifestyle and a lack of physical activity. Self-esteem is an essential component in the development of personality and just like physical activity, very important in adolescence. The main objective of this study is to examine the correlation between physical activity and the degree of self-esteem in adolescents and to determine whether there is a difference in the correlations between body function and self-esteem in the younger and older age groups of adolescents, or whether there is gender difference. The study included 203 adolescents, aged 15 to 19, including 155 girls and 48 boys, and was conducted in Zagreb in the period from October 2017 to April 2018. The study used "Fels Physical Activity Questionnaire for Children" (Fels PAQ for Children), a standardized questionnaire for assessing the physical activity of children and adolescents, and the Rosenberg Self-esteem Scale (RSE), which is a one-dimensional scale that reliably measures global self-esteem. The obtained results showed that there is a positive correlation between physical activity and self-esteem in adolescents. In the total sample, the coefficient of determination was r2 = 0.055, which suggests that 5.5% of self-esteem levels in adolescents of both sexes can be explained by the level of physical activity. The study also showed that there is a difference in the correlation between the index of physical activity and self-esteem according to gender. In boys, the correlation is much higher than in girls, so for the male gender the coefficient of determination is r2 = 0.138, which results in 14% of self-esteem in male sex being explained by the level of physical activity, while in the female gender this study did not establish the statistically significant existence of the correlation of the investigated indices. The correlation coefficient was also higher in the age group of middle adolescence in both sexes, and this was especially evident in the male gender. In this age group, in boys, the coefficient of determination r2 was 0.277 or nearly 30% of self-esteem variance could be explained by the level of physical activity. Several conclusions emerge from the results. Older adolescent girls have a higher level of self-esteem than mid-adolescent girls, while at the level of physical activity there are no statistically significant differences among them. For boys there are no statistically significant differences in the index of self-esteem, nor in the index of physical activity. Physical therapy technicians have shown a slightly higher level of physical activity index, and there is no difference in the level of self-esteem between the respondents studying different courses. Research in this direction, on a wider sample and on a number of variables, should be pursued in order to reinforce the effects of physical activity on the psychological dimension of the human body in order to raise awareness of its importance and promote physical activity across the population, especially among adolescents.