Presented here is the first reported case of natural killer (NK)/T-cell lymphoma associated with lactic acidosis (LA) and hypoglycemia. LA and hypoglycemia are rare complications of non-Hodgkin's lymphoma. A 28-year-old male patient with NK/T-cell lymphoma had a relapse after 14 mo of initial remission and was admitted to the hospital because of altered mental status. He developed severe LA (pH, 7.17; lactate, 11.2 mmol/L) and hypoglycemia (42 mg/dL) that was resistant to sodium bicarbonate and glucose infusions. A very brief partial remission was achieved after a cycle of vincristine, dexamethasone, and L-asparaginase was given, but the disease recurred quickly after chemotherapy was discontinued and the patient did not respond to additional chemotherapy. The patient expired at 47 d after relapse. An extensive review of the literature reveals that only 2 of 28 patients have achieved complete remission, and more than 75% of patients died within 1 mo. Furthermore, 90% of previously reported cases had liver involvement. The case described here indicates that non-Hodgkin's lymphoma-induced LA portends a poor prognosis.