Mast cell disease (MCD), a proliferation of mast cells (MC), is occasionally associated with hematologic malignancies, Neoplastic NIC have activating c-kif mutations, c-kif is a receptor tyrosine kinase required for the development, proliferation, and survival of MC. Interaction of c-kit with its ligand stem cell factor induces dimerization, receptor phosphorylation, and signal transduction. The most common c-kit mutation detected in neoplastic MCD is Asp816Val, which results in ligand-independent autophosphorylation of the receptor leading to MC proliferation, We describe the rare occurrence of MCD associated with acute myeloid leukemia, report a novel c-kit mutation Asp816 His, and discuss the pathogenesis of MCD associated with hematologic malignancies. (C) 2000 Wiley-Liss, Inc.