A 72-year-old man was admitted to a general hospital with progressive liver dysfunction, hypokalemia, hyperglycemia, and nodules in the lung and liver and then transferred to our institution on the seventh hospital day. Plasma levels of adrenocorticotropic hormone (ACTH), cortisol, and neuron-specific enolase concentrations were extremely high. He developed acute liver failure, his consciousness and general condition deteriorated rapidly, and he died on Day 11. At the postmortem examination, he was found to have extensive metastases from small-cell lung cancer, including advanced hepatic metastases. This is the first reported case of acute liver failure caused by metastases derived from an ACTH-producing pulmonary small-cell carcinoma.