An emotional state or mood characterized by one or more of these symptoms: sad mood, low energy, poor concentration, sleep or appetite changes, feelings of worthlessness or hopelessness, and thoughts of suicide.

Until recently, it was thought that children and adolescents could not suffer from clinical depression. It was assumed that children were not physically or psychologically mature enough to develop symptoms of depression and that adolescents with mood difficulties were simply going through "growing pains." However, several investigations have shown that if appropriately evaluated, children and adolescents do suffer from depression. We will refer to clinical depression that presents with severe symptoms as major depressive disorder (MDD) and depression that has moderate, chronic symptoms as dysthymic disorder (see below for specific criteria). Depression is relatively common; the prevalence (number of cases in one year) of MDD and dysthymic disorder combined is approximately 2% for children and 6% for adolescents...