Introduction: Unhealthy nutrition results from inappropriate eating behaviours that lead to changes in body weight. Consuming excessive amounts of salt, sugar, carbonated drinks, alcohol combined with physical inactivity causes overweight or obesity. In order to prevent incorrect nutrition, it is necessary to prevent overnutrition and to promote health-promoting behaviours that should be targeted at specific groups of the society. Such initiatives may limit or even exclude the emergence of incorrect nutrition which contributes to an increase in the incidence of lifestyle diseases. Objective: The aim of the article is to present and discuss the forms of spending free time, participation in physical education classes, and dietary habits of third-year secondary school students in the city of Bielsko-Biała (Poland). Materials and methods: An original questionnaire entitled “My health – something I care about” was used for the study. The questionnaire included questions about the diet, forms of spending free time, and participation in physical education classes at school. Results: Based on the questionnaire findings, watching TV is the most common form of spending free time (37% boys and 32% girls). Only 7% of girls and 18% of boys chose participation in sports as a form of spending their free time. 28% of boys and as much as 39% of girls admitted that they did not participate in physical education classes at school. The type of drinks consumed by secondary school pupils was significantly dependent on their gender. Regarding the type of lunch, sweet buns are chosen by 31% of boys and 23% of girls. Fruit is declared as their preferred lunch snack by 28% of the surveyed girls and only 2% of boys. Conclusions and discussion: The study has shown that there are many abnormalities in the diet of adolescents. The widespread belief that a slim figure is an asset nowadays prompts many young people to use various weight loss diets or fasting which, if used excessively, can pose a threat to the developing body systems. Information gathered from the respondents also shows that they do not have sufficient physical activity. Secondary school pupils increasingly choose passive recreation because physical activity does not give them as much satisfaction as, for example, playing computer games.