Compared to primary thrombocytosis such as that caused by essential thrombocytosis, reactive thrombocytosis is generally regarded as benign. However, reactive thrombocytosis has infrequently been reported to cause severe and even fatal complications. Two fatal cases of reactive thrombocytosis and iron deficiency anemia associated with peripheral/pulmonary vascular and cerebrovascular thrombosis are described. The literature on thrombosis and reactive thrombocytosis associated with iron deficiency anemia is reviewed.