Endogenous lipid pneumonia was present in 19 of 27 opossums (Didelphis virginiana) trapped in the vicinity of Baton Rouge, Louisiana. The severity of lesions varied from small pleural and subpleural aggregates of foamy macrophages with minimal disruption of pulmonary architecture to large nodular accumulations of foam cells with cholesterol clefts and localized emphysema. The cause of the lipid pneumonia may be related to pulmonary nematode parasite infections, which were evident in 13 of the affected animals.