The aspiration of stomach contents is a common clinical problem of concern to all physicians. Its consequences are varied, depending on the amount and distribution of the aspirate, its pH, and the presence or absence of food, particulate matter, and bacteria. Because multiple factors are involved, aspiration of stomach contents can lead to several distinct syndromes of pulmonary injury, all of which unfortunately have been labeled "aspiration pneumonitis." We review the pathophysiology of each of these syndromes and discuss important diagnostic and therapeutic consequences.