The purpose of this report is to remind clinicians of the risk of the simultaneous occurrence of neuroleptic malignant syndrome (NMS) and lithium intoxication. A 39-year-old female with bipolar I disorder was admitted to our psychiatric ward due to relapse of a manic episode and a suicide attempt in which she had ingested 20 to 30 tablets of lithium (300 mg/tablet) 12 hours before admission. Except for intramuscular injection of 5 mg of haloperidol 30 minutes after admission, the patient received no antipsychotic drugs during her hospitalization. Six hours after admission, she began to show symptoms of NMS. Lithium intoxication was also found. Within a week, her condition had stabilized with no neurological complications or cognitive deficits noted during the following 4 months. Discussed in this case report are the risk factors of NMS found in this patient, drug interactions of lithium and antipsychotic agents as related to NMS, and problems in clinical management.