Examining peripheral blood smears provides valuable information in the diagnosis of anaemia despite large inter- and intraobserver variation. The classification of anaemia is usually based on the average erythrocyte size, referred to as the mean corpuscular volume (MCV). Microcytosis indicates a reduced haemoglobin synthesis caused by either an iron deficiency or haemoglobinopathy, a congenital disorder. Macrocytosis is the result of a disruption to the division and maturing of proerythroblasts in the bone marrow, due, for example, to vitamin B12 (folic acid) deficiency or excessive alcohol use. Furthermore, a high number of reticulocytes in the blood indicates an increased production of erythrocytes whereas a low total indicates an inadequate production level. In addition to the case history and the physical examination, the MCV and number of reticulocytes can provide guidance with respect to further diagnostic investigation.