Introduction:
Treatment of obesity in adolescents is often ineffective, thereforer factors should be discovered which motivate young people to follow weight loss methods recommended by experts.

Aim:
The objective of the study is to analyze the relationship between the use of diet by 13-year-olds with excess body weight and selected psychosocial factors.

Material and Methods:
The study was conducted in 2008 in a prospective cohort of 605 children. The 13-year-old adolescents received questionnaires by mail which contained questions concerning eating habits, dieting, family environment, social support, self-efficacy and quality of life. School nurses measured the height and weight of the students. BMI was calculated, and the group of young people with excess body weight (n = 116) was selected. Statistical analysis included chi-square test and one-way analysis of variation ANOVA.

Results:
Every fourth respondent with excess body weight applied a diet (27% girls, 20% boys, p <0.05), twice as often as adolescents with obesity than with overweight (32% vs. 16%, p <0.05), while 14% of girls and 36% of boys did not see the need for dieting. Young people who were aware that they should diet, but did not do so (50% of respondents), evaluated relationships in their families, rarely received positive reinforcement from their parents, had less social support, self-efficacy and the lowest quality of life in more negative terms compared to the remaining adolescents in the study.

Conclusions:
In order to help obese adolescents to lose weight, their parents should provide them with emotional support and care to increase their sense of self-efficacy.