Aim. The aim of the study is an evaluation o f the occurrence and dynamics o f depression during mid-adolescence. It was conducted in prospective studies on a representative group of gymnasium school adolescents in large towns. 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 the years 2001, 2002, 2003. Results. The point-prevalence of depression was respectively 24.6%, 24.5% and 26.6% for 13, 14 and 15 year-olds. The spread-out rate o f depressive disorder in the studied group turned out to be relatively stable. 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 midadolescent population, depression is a disorder of an unequivocal nature.