The bipolar mood disorder is the third of the major psychiatric afflictions that are discussed in this series, after schizophrenia and depression. The patient´s mood swings from one extreme pole to the other; that is why in the past the patients were described as manic depressive. Alternatingly euphoric and depressed periods occur. In some patients this happens several times a year. The cause(s) of the illness are still obscure. Psychotherapy is hardly able to influence its course; in the pharmaceutical approach continuous administration of lithium salts is the mainstay of treatment. Ten thousands of people in the Netherlands suffer from this affliction that severely debilitates their mental and social functioning.