Major Depressive Disorder is a recurrent illness. While each episode usually responds to treatment it tends to be a chronic disorder and patients do tend to relapse (the condition deteriorates again before an episode is completely resolved).

Recurrences of major depressive episodes are also common and for a patient who has required hospitalisation for the initial episode (i.e. severe depression) there is a 30 - 50% chance of recurrence within the first two years and a 50 - 75% chance of recurrence within 5 years.

The likelihood of relapse or recurrence is much less in those who continue to use prophylactic psychopharmacological treatment (i.e. either continue with antidepressant medication or make use of a mood stabilising drug).

Usually as more depressive episodes are experienced, the time between episodes decreases and the severity of the depression increases. Men are more likely than women to experience a chronically impaired course. A poor prognosis is also more likely with a co-existing anxiety, dysthymic or substance abuse disorder.