The association of mast cell diseases and some hematologic malignancies, usually myeloproliferative disorders, myelodysplastic syndromes, and acute leukemia is well recognized. We report the case of a patient with telangiectasia macularis eruptiva perstans, a rare form of cutaneous mastocytosis, and multiple myeloma, an association that has been described only twice in the literature. Parallel improvement of both conditions was observed under chemotherapy regimens for multiple myeloma. Pathogenesis remains unclear, although the abnormalities in the c-kit pathway may play a role in the proliferation of cells from both lineages. (J Am Acad Dermatol 2000;43:972-4.)