Depression is a common illness which affects some 3% of the population per year. At least 25% of those with marked depression do not consult their general practitioner and in half of those who do the illness is not detected. Depression is easy to recognize when four or five of the core symptoms have been present for 2 weeks which often coincides with some occupational and social impairment. The core symptoms are depressed mood, loss of interest or pleasure, loss of energy or fatigue, concentration difficulties, appetite disturbance, sleep disturbance, agitation or retardation, worthlessness or self blame and suicidal thoughts. A diagnosis of depression is made when five of these core symptoms, one of which should be depressed mood or loss of interest or pleasure, have been present for 2 weeks. Four core symptoms are probably sufficient. Response to antidepressants is good in those with more than mild symptoms. When there are only few or very mild depressive symptoms evidence of response to antidepressants is more uncertain. Antidepressants are effective, they are not addictive and do not lose efficacy with prolonged use. The newer antidepressants have fewer side effects than the older tricyclics, they are better tolerated and lead to less withdrawals from treatment. They are less cardiotoxic and are safer in overdose. Antidepressants should be used at full therapeutic doses. Treatment failure is often due to too low a dose being used in general practice. It may be difficult to reach the right dose with the older tricyclics because of side effects. To consolidate response, treatment should be continued for at least 4 months after the patient is apparently well. Stopping the treatment before this is ill-advised as the partially treated depression frequently returns. Most depression is recurrent. Long-term antidepressant treatment is effective in reducing the risk of new episodes of depression and should be continued to keep the patient well.