4 cases are reported. Symptoms are mainly those of associated diseases or disorders which are most frequently found to be respiratory tract infections and other infectious diseases, central nervous system disorders, impaired general condition, and feeding or swallowing difficulties. Usually there is a combination of two or more of these disorders. Physical examination reveals no specific signs. There is usually some degree of nutritional disturbance. Rapid respirations are frequently recorded. Fever, if present, is usually low-grade and the chest signs are those of the usually associated respiratory infection. The roentgen-ray is of the greatest diagnostic value but may often be difficult to interpret due to other pulmonary diseases. A lack of change over a long period of time in serial chest rqentgen-rays is an important point. Sputum examination for free oil droplets or large phagocytic monocytes containing fat or oil should always be done in suspected cases. Interval vital capacity estimations are recommended. The gross and microscopic pathology is briefly descr. Final diagnostic proof is obtained by identification of the offending agent by chemical analysis of the oil or lipoid in the involved lung tissue. Scrapings from the cut surface of lungs in all cases of lung examinations are streaked and stained for fat at the time of autopsy. If the above test is positive, qualitative and quantitative chemical analysis for fats should be done. The pathogenesis of oil aspiration pneumonia and pneumolipoidosis of exoge-nous nature and pneumolipoidosis of endogenous nature is briefly touched upon. The best therapy is prevention. Recommendations on prophylaxis are made.