Pyoderma gangrenosum is a papulovesicular skin disorder commonly associated with underlying systemic disease, but rarely with the myeloproliferative syndromes. A case of rapidly progressive pyoderma is cited in a 77-year-old white man who had no other evidence of disease aside from macrocytic anemia. Bone marrow biopsy revealed proliferation of fibroblasts and a dense reticulin network consistent with myelofibrosis. Response of the pyoderma to steroid therapy was dramatic. Although pyoderma gangrenosum is more commonly associated with inflammatory bowel disease and rheumatoid arthritis, this is the fifth reported case of its coexistence with idiopathic myelofibrosis.