Overweight and obesity is an epidemic that the world has been battling for decades. They are also significantly associated with the risk of chronic non-communicable diseases whose incidence and prevalence in the world is still growing. Two of the four most prominent risk factors in the occurrence of overweight and obesity and in the occurrence of chronic non-communicable diseases are inadequate diet and insufficient level of physical activity. These two factors are also the two factors we can influence the most. Eating habits are a complex and still insufficiently researched area that is influenced by a number of factors, of which knowledge stands out as one of the most significant. Adolescence is a period in life characterized by great changes. It is extremely important because in this period of life different habits that last a lifetime are formed, developed and further strengthened. Examination of eating habits and physical activity is the first step in taking effective measures so the aim of this study was to examine the level of nutrition of adolescents, their eating habits, dietary knowledge, level of physical activity and lifestyle, level of self-efficacy and barriers to change in possible improvement of eating habits. The aim was also to examine food safety knowledge and hygiene practices and to examine whether there are differences according to gender and nutritional status. The aim was also to examine the connection between nutrition knowledge and eating habits, but also the connection between knowledge and nutrition and physical activity. The research was conducted on 1520 students (of which 646 female and 874 male students) of the second grade of seventeen high schools in the City of Zagreb an average age of 16.75 (0,47). A questionnaire was used and validated on adolescents of similar age in Italy (Turconi et al., 2003 and 2008). The questionnaire consists of nine segments. The collected data was processed by the statistical software package Statistica - version 13.3 and Microsoft Excel 2016. After the basic descriptive statistics, the Student's t-test for gender differences and univariate analysis (ANOVA) were used to determine differences between subjects of different nutrition categories, Pearson's correlation coefficient for determining the correlation of variables and regression analysis to determine the contribution of individual variables to eating habits. The level of statistical significance was set at p0,05. Male students have a significantly higher body mass index than female students. On average there is 7% thin, 76% normal weight, 14% overweight and 3% obese students in total. There is a higher incidence of thinness in girls, and overweight and obesity in boys. Satisfactory eating habits were shown by less than half of the respondents with no differences by gender or nutrition category. Within the segment, differences were found in certain questionnaire items. Girls are statistically significantly less likely to eat breakfast and consume all three meals a day, while at the same time the breakfast they consume is healthier. They also consume less alcoholic beverages and sweetened juices, their diet contains less fat, but they also consume significantly less dairy products. Differences within this segment by nutritional status were found in the consumption of desserts after meals, alcoholic beverages, snack content, beverages between meals, dairy products and intake of water. The intake of fruits and vegetables in all groups is extremely small. In terms of physical activity less than half of adolescents live a satisfactorily active life. More than 43% of them spend more than 3 hours a day in front of a screen; young men and normal weight are significantly more active. Excellent and satisfactory knowledge i.e. understanding of basic terms related to food and nutrition was shown by the largest number of adolescents, while the level of more detailed knowledge of food is unsatisfactory in 42% of students. Despite lower levels of knowledge on food safety, the hygienic practices of a large number of adolescents related to food safety are satisfactory. Significantly higher level of knowledge was shown by girls in all knowledge segments. No differences according to the nutrition status were found. A high level of self-efficacy was shown by more than 80% of adolescents. Nearly 70% of adolescents were found to have a very small number of barriers to change related to eating behaviors. Differences by gender and nutrition status were not found. A statistically small but significant association of dietary knowledge and eating habits was found. The association between knowledge and physical activity and knowledge and nutrition were not found. Dietary knowledge, self-efficacy, barriers to change, and food hygiene have been shown to be significant predictors of eating habits. The general conclusion is that there is a need to increase levels of physical activity and knowledge given that a high level of knowledge prevents unhealthy eating habits. The conclusion is also that the examined segments can significantly contribute to the improvement of habits, but since they explain only a small part of this complex behavior (10% variance), additional research is needed to identify the remaining factors and their impact on eating habits.