Granulocyte macrophage-colony-stimulating factor (GM-CSF) is a cytokine used to stimulate the growth and maturation of granulocytes and macrophages in a variety of clinical settings. Reported cutaneous side effects of GM-CSF therapy include both local reactions at the site of injection and diffuse eruptions. In this report we describe the clinical and histologic features of three patients who had a widespread macular-papular eruption after GM-CSF therapy to stimulate bone marrow recovery. In all three patients the eruptions occurred within 3 days of starting GM-CSF therapy and resolved after the infusion ended. Histologic features of the eruptions included a mixed infiltrate of lymphocytes, eosinophils, and neutrophils, primarily in the papillary dermis. In all three cases there was an increase in the number of dermal macrophages, and in two cases there was a striking increase in the size of dermal macrophages, many of which contained ingested elastin. We report these cases to alert the reader that alteration in number or size of dermal macrophages is a clue to the diagnosis of GM-CSF-induced dermatoses. A review of the literature of cutaneous side effects of GM-CSF is included.