The clinical presentation and course of chemical pneumonitis after inhalation of gastric contents ranges from mild and self-limited to severe and life-threatening, depending on the nature of the aspirate and the underlying condition of the host. In the absence of witnessed inhalation of vomit, diagnosis is difficult and requires a high index of suspicion in a patient who has risk factors for aspiration. In the absence of an obvious predisposition, the abrupt onset of a self-limited illness characterized by dyspnea, cyanosis, and low-grade fever associated with diffuse rales, hypoxemia, and alveolar infiltrates in dependent lobes should suggest aspiration. Treatment consists of supportive care with high-flow oxygen and volume replacement. Bacteria usually play no role in the initial lung injury, and antibiotics should be withheld until there is evidence of superinfection. Prophylactic corticosteroids should not be used. Preventive measures should be employed in patients at high risk for aspiration. Patients with unexplained chronic respiratory syndromes should be evaluated for gastric regurgitation and aspiration.