Exogenous lipoid pneumonia is an uncommon condition resulting from aspirating or inhaling fatlike material, such as mineral oil found in laxatives and various aerosolized industrial materials. These substances elicit a foreign body reaction and proliferative fibrosis in the lung. Because symptoms are absent or nonspecific and the roentgenographic findings simulate other diseases, exogenous lipoid pneumonia is often unrecognized. Yet, appropriate historical inquiries and simple laboratory tests can lead to the correct diagnosis, removal of the offending agent, and, potentially, improvement in lung function before serious complications develop.