Aims: The aim of the study was to examine trends in adolescent depression and anxiety symptoms from 1997 to 2006, using four time-points (1997, 2000, 2003, and 2006), and adolescent mental health service use in the same period, using three time-points (1997, 2000, and 2006). Methods: Four cross-sectional population-based samples of 14- and 15-year-old students, attending the compulsory 9th and 10th grades of the Icelandic secondary school system, completed questionnaires relating to mental health. In total, 21,245 students participated in the four studies. Results: Anxiety symptoms increased significantly for both boys and girls, throughout the period from 1997 to 2006. Depressive symptoms increased significantly for girls, while there were no significant changes in depression among boys. During the same time period, the proportion of adolescents who visited healthcare specialists, i.e. psychiatrists, psychologists and social workers, increased significantly. The results revealed that regular visits (six times or more during 1 year) to psychiatrists and psychologists increased significantly over the same period among girls but not among boys. Conclusions: The findings show that symptoms of depression and anxiety have increased among adolescents in Iceland. Future work would benefit from further research into the trends in risk and protective factors associated with these outcomes. The findings call particular attention to the increasing risk for depression and anxiety symptoms among girls.