The margin between the therapeutic benefit and toxic effects of lithium is small. Lithium toxicity may occur in a number of situations: (i) if lithium is taken in too large a dose; (ii) if excretion of the drug by the kidneys is inadequate; and (iii) if lithium concentrations increase in cells because of negative sodium balance or drug interactions. The features of this syndrome are primarily exhibited in the nervous system, and include coarse tremor, increased reflexes, ataxia, increased muscle tone, seizures and coma.Treatment depends above all on the patient's clinical state, but also on the duration of previous lithium exposure, serum lithium concentration, renal lithium clearance, and the extent of dehydration.Gastric lavage may be necessary if there are obtunded laryngeal reflexes, but is usually of no value if used more than 4 hours after lithium ingestion. Saline diuresis may be needed to increase renal lithium excretion, but dialysis may be necessary if lithium is not being excreted adequately. Peritoneal dialysis and continuous arteriovenous haemodiafiltration reduce serum lithium concentrations more slowly than haemodialysis, which is still the most frequent measure employed in severe cases, despite some doubts about its value. Haemodialysis is normally used if patients have clear neurological symptoms and signs, particularly if these are deteriorating, if lithium clearance is less than 7 ml/min, and serum lithium concentrations are above 3 mmol/L.