This paper describes the organization of a lithium out-patient clinic before discussing a follow-up study over a period of 29 months. The results of this follow-up study are indicative of the prophylactic effect of lithium in unipolar and bipolar depressions. A separate section is devoted to the influence of lithium on the hypothalamus-pituitary-thyroid axis. The results of this endocrinological study indicate that thyroid function should be determined not only before but also during lithium medication. Finally, it is recommended that specialized lithium out-patient clinics be established in view of the nature of this agent and the need for strict supervision. The function of these out-patient clinics and the collaboration with family doctors is elucidated.