Aim. The aim of the study is to evaluate the occurrence and dynamics of depression during mid-adolescence. It is conducted in prospective studies on a representative group of high school students in a large town. Method. In a two-stage draw, a representative group of 1737 13 year-old adolescents was chosen. They were surveyed by the Krakow Depression Inventory (KID) subsequently in 2001, 2002 and 2003. Results. The point prevalence of depression was respectively 24.6%, 24.5% and 26.6% for 13, 14 and 15 years olds. The spread-out rate of depressive disorder in the studied group turned out to be relatively sTab. Conclusion. Depression is more common amongst mid-adolescent girls than boys. Dynamics of the disorder, when studied throughout the three years show that amongst the mid-adolescent population, depression is a disorder of heterogeneous nature.