In the Netherlands, lithium is the mood stabilizer of choice for patients with bipolar disorder. Long-term treatment with lithium can only be implemented safely with frequent and appropriate monitoring of serum lithium concentrations. Here we use 3 cases to illustrate that severe complications can arise when careful monitoring is not performed: a 47-year-old woman with symptoms of a lithium intoxication with therapeutic plasma levels; a 73-year-old woman with chronic lithium intoxication; and a 56-year-old woman with end-stage renal failure after many years of probable toxic lithium levels.