Lithium has a narrow therapeutic index and poisonings are mostly due to chronic overdose secondary to an impaired renal elimination. Neurologic toxicity is predominant and poisonings can be classified into three grades according to the severity of symptoms. Lithium serum concentrations must be interpretated according to the type of poisoning (acute, acute-on-chronic or chronic) which explains the kinetic variations. Apart from symptomatic measures, the major therapeutic objective is to enhance lithium elimination either by administration of sodium salts if renal function is normal or by haemodialysis. Haemodialysis is especially indicated in patients with chronic overdose presenting severe symptoms, an increased serum lithium half-life and an impaired lithium renal elimination.