Three patients with "adult" Gaucher's disease with severe pulmonary involvement are described. The clinical course of these patients was characterized by hepatosplenomegaly in infancy, followed by the juvenile onset of dyspnea culminating in pulmonary failure and death. Pathologic examination of the lungs in these patients revealed not only massive infiltration of alveolar walls by Gaucher's cells but also clumps of these cells filling alveolar spaces and obliterating functional air exchanging tissue. The lack of neurologic involvement in these cases delineates them from the "juvenile" forms of Gaucher's disease whereas the malignant course and pulmonary involvement were atypical of the "adult" form. The severity of this type of Gaucher's disease makes it a good candidate for prenatal enzymatic diagnosis.