Hemodialysis is the usual recommended treatment for severe lithium intoxication when emergent extracorporeal lithium removal is necessary. Intermittent hemodialysis has been chosen most frequently, however it has disadvantages such as postdialysis rebound elevation in lithium concentration, hemodynamic instability, tendency to develop hypovolemia and deteriolate renal function. On the other hand continuous hemodiafiltration (CHDF) offers an advantage of slow sustained removal of lithium without the adverse effects of conventional hemodialysis. The following is a report of a case of severe chronic lithium intoxication successfully treated with CHDF. A 69-year old woman, who had been diagnosed with manic-depressive psychosis 18 years previously, was transferred to our ICU because of unconsciousness during lithium maintenance therapy (lithium carbonate 800mg/day). On arrival her consciousness level was Japan Coma Scale 100 and the pulse rate was 30beats/min. Since she had a past history of cardiac failure, we conducted CHDF to accelerate lithium elimination. CHDF was continued for 64 hours and thereafter her condition improved uneventfully.