Objectives: Thrombocytosis is a frequent reason for hematological consultation. The etiology of thrombocytosis is classified as primary and secondary. While primary is result of clonal expansion due to myeloproliferative disorders (MPD), secondary thrombocytosis occurs due to a reactive state and regresses when that is resolved. Iron deficiency (IDA) is a frequent cause of reactive thrombocytosis in outpatients. The aim of this study was to investigate whether IDA and thrombocytosis mask a MPD in patients presenting with these complaints. Materials and Methods: This prospective study included 50 patients who were admitted to our hematology clinic with thrombocytosis and IDA. Causes of reactive thrombocytosis such as infections, surgery, malignancies, inflammatory diseases, asplenia, and pregnancy were excluded. All patients received oral or intravenous(iv) iron replacement as anemia treatment. Anemia and thrombocyte (PLT) count were measured and recorded initially and at the end of first month. JAK2 V617F (JAK2) mutation was also checked due to MPD investigation. Results: Hemoglobin (Hb) and ferritin levels increased in the first month of treatment (p<0.001). Higher ferritin levels were recorded in patients treated intravenously. A significant decrease was detected in PLT count following iron replacement (p<0.001). In 2 female patients no significant decrease was achieved in PLT count and the level persisted despite increases in Hb and ferritin level. Positive (JAK2) mutation was detected and MPD was diagnosed in these 2 patients. Conclusion: Clinicians should investigate patients presenting with IDA and thrombocytosis in terms of reactive causes such as infections, asplenia, malignancies, and inflammatory diseases. Furthermore, MPA should be kept in mind as well as other reactive causes if thrombocytosis persists despite successful IDA treatment.