Dysthymia is a mood disorder characterized by chronic  depression  that lasts for at least two years, but is not as severe as major depression. Although it causes significant distress or some impairment in function of school or work performance, socially or otherwise, it is not as severe as the impairment caused by major depression.

Dysthymia typically begins gradually during early adulthood, and patients usually have trouble pointing out precisely when they first became depressed. It is common for patients to consider their depression normal. Dysthymia may be associated with other mental illnesses (e.g., anxiety disorders, substance abuse).

Improper levels of certain brain chemicals seem to be linked to dysthymia. The disorder is more common in adult women and seems to have a genetic component, making it more common in people closely related to patients with depression. Stressful life situations (e.g., discrimination, poverty, chronic illness) may also be associated with the condition.

The symptoms of dysthymia include sadness, hopelessness, despair or pessimism (believing everything will turn out badly), fatigue or loss of energy, and substantial changes in appetite.

Before an individual can be diagnosed with dysthymia, a physical examination must be performed by a physician to rule out other medical conditions that may be causing the symptoms (e.g., thyroid malfunction). Diagnosis is then made by a mental health evaluation performed either by a physician or another mental health professional. Normal responses to grief need to be ruled out. It is possible for both dysthymia and major depression to be diagnosed, resulting in what is referred to as double depression.