We report the autopsy findings in a case of malignant an gioendotheliomatosis proliferans. Neoplastic cells stained positively for leukocyte common antigen, factor VIII-related antigen, and IgG by the indirect peroxidase-antiperoxidase technique. The authors speculate that malignant angioendotheliomatosis proliferans represents a distinctive type of neoplasm that appears either to exhibit bidirectional lymphoid and endothelial diferentiation or to consist of an heterogeneous population of cells.