Aim. The aim of the study was to examine the selected nutritional behaviours of junior- high school students with different body mass from the Bialski school district. Basic procedures. Based on international standards for the subjects’ BMI, they were divided into three groups: underweight, norm, and overweight or obese. We used our own personally designed questionnaire to evaluate nutrition behaviours. Results. Body Mass Index (BMI) for most of the subjects, both girls (69.84%) and boys (79.9%) was within the norms. The most commonly noted source of knowledge about health was the media, and the least popular – teachers. Overweight and obese youth declared abiding the principles of maintaining a healthy lifestyle less frequently than the rest. More than 65% of the subjects consumed 3 to 5 meals a day. The most common mistakes in eating habits are: irregular eating, snacking in-between meals, frequently eating fast-food meals. Conclusions. The studied youth declared that they adhere to the principles of a healthy lifestyle, however, abnormal nutritional behaviours were observed related to, among others: lack of regularity in eating meals, snacking in-between meals and frequent consumption of fast-food meals. The results of the study indicate the need for education about maintaining a healthy lifestyle and its impact on health.