The COVID-19 virus has suddenly changed the course of people's daily lives on a global scale. Croatia faced this virus for the first time in February 2020, when the first case of a person infected with the COVID-19 virus was recorded. Considering the potential danger of the virus, it was necessary to maintain social distance, and thus the whole world, the World Health Organization, the EU Parliament and the headquarters of the Republic of Croatia made a decision on social isolation. In Croatia, the isolation lasted from March 2020 to May 2020. The aim of the research in this paper was to find out how the younger population in Croatia perceives the psychological consequences of social isolation during the COVID-19 virus pandemic. Therefore, the respondents evaluated their own mental state before, during and after the pandemic, i.e. during social isolation. The results of the research have shown that the mental state of the subjects was moderately worse during social isolation, that is, the feeling of anxiety and stress increased during that period. Today, the respondents are less worried about the coronavirus due to the acquired knowledge and experience with the pandemic and adaptation to the new situation.