We have encountered four patients in whom a localized area of exogenous lipoid pneumonia appeared to undergo malignant degeneration. These four patients, two of whom were from the University of Cincinnati Medical Center and two from other institutions, plus six similar patients culled from the literature, form the basis of this report.In each case, the malignant process occurred in the same location in the lung as the lipoid granuloma. In no instance was the malignant change recognized in its early phase, but in several cases in which the diagnosis of lipoid pneumonia had been established, accelerated spread of the lesion eventually led to the recognition of the superimposed carcinoma.