Lithium treatment, employed in western countries by 1 – 1.5 persons out of every 1,000 in the population, might with advantage be used more for mania and as a supplement to antidepressants in treatment refractory depressions. Prophylactic efficacy is as good in unipolar depressive as in bipolar illness. Start and discontinuation of prophylactic treatment is decided jointly by patient, spouse and psychiatrist. Treatment intensity (dosage, serum level) should be fine-tuned to lowest effective level. Treatment safety is ensured by observation of guidelines and precautions, and again cooperation between the psychiatrist and the carefully instructed patient and family is essential.