We report a case of acute eosinophilic pneumonia (AEP) apparently caused by the resumption of smoking. A 38-year-old woman was admitted to our hospital because of dry cough, high fever and chest pain. Arterial blood gas analysis revealed pronounced hypoxemia and chest X-ray film disclosed diffuse bilateral infiltrate throughout all lung fields. Eosinophils (43.7%) were significantly increased in bronchoalveolar lavage fluid (BALF). The patient was treated with pulse therapy consisting of methylprednisolone and improved quickly. AEP was diagnosed on the basis of BALF findings and the patient's clinical course. Prior to and after her illness, the only noteworthy change in the patient's environmental setting or habits was the resumption of smoking, 3 days after which the symptoms had appeared. We reasoned that the onset of AEP in this patient was strongly related to the resumption of smoking.