We developed anecdotal evidence that parenteral iron therapy is associated with a characteristic pattern of iron staining in bone marrow aspirate smears. In this pattern, uniform blue granules are observed within reticuloendothelial cells/stromal cells with Prussian blue staining, many times in curvilinear arrays. To test this hypothesis, marrow cases submitted for morphologic evaluation to our laboratory during an approximate 2-month period in 2006 were assessed for this pattern, and, when it was observed, clinical information was sought to determine if the patient had received parenteral iron. Fourteen cases were identified that displayed the pattern of interest. In 10 of these cases, the pattern was widespread (numerous granules present within virtually all marrow spicules), whereas in 4 cases, the pattern was seen only focally. In all cases in which the pattern was widespread, patients were found to have received parenteral iron at some point before the aspiration procedure. Our findings indicate that parenteral iron therapy is associated with a characteristic pattern of iron staining in bone marrow aspirate smears.