Acute lithium intoxication may occur in circumstances causing kidney failure, when using lithium chronically. This situation may lead to neurological symptoms with coma, gastrointestinal disorders with diarrhea, cardiovascular symptoms with hypotension and metabolic symptoms with hypercalcemia. Nephrogenic diabetes insipidus may also develop. We report the case of a 69-year-old woman suffering from unipolar manic-depressive psychosis and treated by lithium for 10 years. This case highlights the need to monitor serum lithium levels in patients on long-term lithium regimens, especially in circumstances involving dehydration.