Because of the new epidemiological studies during the past two decades our knowledge concerning child and adolescent psychiatric disorders has grown up. There exists data concerning the distribution of different disorders in the community. The development in the methodology of child psychiatric investigation has made it possible to study also the risk factors and prognostic features of child psychiatric disorders. In this paper risk and prognostic factors of various child psychiatric disorders are reviewed. All the findings from studies made in different countries are not suitable as such in Finland. No large scale epidemiological studies concerning the risk and prognostic factors of various child psychiatric disorders are available in Finland. The cohort-66 study offers a possibility to elucidate also these factors.