Lithium therapy has various neurologic cardiovascular, and renal side effects. Lithium intoxication with a serum lithium level of greater than or equal to 3.5 mEq/l is considered potentially lethal and hemodialysis therapy is recommended. We reviewed the clinical course and therapy of 55 patients with lithium toxicity seen during a 6-year period. Forty-two patients had acute lithium intoxication following the ingestion of an overdose. In 13 patients, toxicity developed during maintenance therapy with the drug. The patients with acute intoxication had significantly milder symptoms than those with chronic intoxication. Ten patients with acute intoxication had a serum lithium concentration of 3.5 mEq/l or higher. None of these 10 patients had severe neurologic or cardiovascular symptoms. Five patients were treated with hemodialysis and 5 patients were not. Serum lithium concentration did not differ between the two groups (4.7 +/- 0.7 and 5.7 +/- 1.0 mEq/l, respectively). No patient in either group died or suffered permanent sequelae of lithium toxicity. In conclusion, patients with acute lithium toxicity frequently have mild symptoms, despite potentially lethal levels and may not require hemodialysis therapy. On the other hand, patients who develop toxicity while receiving chronic maintenance therapy are more likely to have severe symptoms. Patients with severe symptoms and serum lithium levels above the therapeutic range should be treated with hemodialysis.