This study wanted to examine the prevalence of internalizing and externalizing symptoms or problem behaviors among adolescents, as well as to examine co-occurrence of symptoms from both mentioned domains. For the purposes of this study, data from the project of UNDP „Support in enforcement of systematic crime prevention work and establishment of Crime Prevention Coordination Unit“ were used and research was done in collaboration with Faculty of Education and Rehabilitation Sciences, University in Zagreb and UNDP took place from year 2008 until year 2011. Except from main goal of this study, which is examining the prevalence of symptoms from all mentioned domains, it was also important to examine if there are gender and age differences in occurring symptoms among adolescents from the examination group. This study included 835 adolescents from high schools in the City of Split and the City of Čakovec. Assessment of prevalence of symptoms from all mentioned domains was assessed with CTC Youth Survey, which high school students fulfilled in their schools with their own acceptance and approval. The results have shown that among adolescents there are the most of those who show co-occurring symptoms from both internalizing and externalizing domain of behavior problems (72,6%). Gender differences were found among prevalence of internalizing symptoms that is more occurring in girls. In addition, the prevalence of co-occurring symptoms is more often related to girls, while boys show more externalizing symptoms than girls. Age differences are partially found, showing that with increase of age, there is also an increase of co-occurring symptoms among adolescents.