Acute eosinophilic pneumonia (AEP) is characterized by idiopathic acute febrile illness, diffuse pulmonary infiltration, severe hypoxemia, and pulmonary eosinophilia. We report a case of AEP associated with intramuscular administration of progesterone as luteal phase support after in vitro fertilization. A 33-year-old woman presented to our emergency room with tachypnea and hypoxemia, complaining of fever and cough for 4 days, and dyspnea for 2 days. The symptoms began 9 days after the first injection of progesterone. Chest radiograph showed bilateral infiltrates, located predominantly in the periphery of the lungs, with blunting of the costophrenic angle. Symptoms and chest radiograph dramatically improved after corticosteroid therapy and shifting the progesterone from an intramuscular form of administration to a vaginal form of administration.