At the global level, the COVID-19 pandemic has left consequences for children and adults in terms of lifestyle, which has manifested itself in the form of an increase in body weight. Adolescents are a particularly sensitive group when it comes to changing habits because of their still insufficiently developed ability to maintain those same habits. The unexpected pandemic exposed them to a greater risk of developing non-communicable diseases that occur as a result of unhealthy habits. The goal of the research is to determine the impact of isolation during the COVID-19 pandemic on the eating and lifestyle habits of high school children in the Primorsko-goranska County and to assess their emotional state. In the research 164 students, between the ages of 15 and 18, were included. Research has shown that isolation due to COVID-19 caused an increase in the proportion of overweight and obesity among high school students due to changes in lifestyle habits and spending more time in front of the screen. Potential psychological problems due to social isolation were also noticed. High school students adhered to the Mediterranean diet to a high extent, which was assessed by the Quality Index of Mediterranean Diet for Children and Adolescents (KIDMED). Implementation of public health programs that promote a healthy lifestyle, and at the same time help prevent non-communicable diseases, could enable adolescents to adhere to a healthy lifestyle more easily.