Thrombocytosis may accompany iron deficiency anaemia (IDA). However, thrombocytopenia is a rare occurrence that might be associated with IDA. A 15-year-old girl presented with IDA related to menorrhagia. Erythrocyte transfusion was given, since the haemoglobin level at presentation was 4.7 g/dL and oral iron supplementation was initiated with ferrous glycine sulphate. On 12th day of iron treatment, platelet count was found to have decreased to a level of 48x10(9)/L. Bone marrow aspiration was obtained in order to investigate the aetiology of thrombocytopenia and revealed erythroid hyperactivity, severe megaloblastic changes, binucleated normoblasts, and decreased number of megakaryocytes. Oral iron replacement therapy was continued and vitamin B12 was added to treatment in view of severe megaloblastic changes in the bone marrow examination. Platelet count normalised and haemoglobin level increased during the follow-up with the replacement of oral iron and vitamin B12.