Anaemia is typically the first clue to iron deficiency, but an isolated haemoglobin measurement has both low specificity and low sensitivity. The latter can be improved by including measures of iron-deficient erythropoiesis such as the transferrin iron saturation, mean corpuscular haemoglobin concentration, erythrocyte zinc protoporphyrin, percentage of hypochromic erythrocytes or reticulocyte haemoglobin concentration. However, the changes in these measurements with iron deficiency are indistinguishable from those seen in patients with the anaemia of chronic disease. The optimal diagnostic approach is to measure the serum ferritin as an index of iron stores and the serum transferrin receptor as a index of tissue iron deficiency. The treatment of iron deficiency should always be initiated with oral iron. When this fails because of large blood losses, iron malabsorption, or intolerance to oral iron, parenteral iron can be given using iron dextran, iron gluconate or iron sucrose.