Objectives:
The aim of the study was to estimate the prevalence of mental health problems in subpopulation of Warsaw adolescents and to identify trends in 2004–2016.

Methods:
The cross-sectional study, conducted every four years, covered the third grade Warsaw middle school students from three Warsaw districts: Mokotów, Ursynów and Wilanów. Sample was randomly selected with the adjustment for cluster selection. The self-administered questionnaire had been completed during school lessons. Indicators were related to following problems: (1) internalizing (symptoms of depression measured by the shortened CES-D scale and other emotional problems, based on subjective assessment); (2) externalizing – coexistence of two out of three types of behaviors (psychoactive substances abuse, being perpetrator of violence and delinquent behavior); (3) mixed.

Results:
In 2016, 42% of youth exhibited symptoms of mental health disorders. These problems more often affected girls (48%) than boys (36%). Between 2008 and 2016, the percentage of young people experiencing internalizing problems increased significantly. This was due to the increase in the prevalence of depressive symptoms. At the same time, there was a significant decrease in the percentage of young people demonstrating externalizing problems. The last result was a consequence of the decrease in substance abuse and violence.

Conclusions:
Growing prevalence of internalizing problems, depressive symptoms and other emotional problems among teenagers indicates an urgent need to develop or adapt effective prevention programs and to improve the access to psychological and psychiatric support.