Iron deficiency is frequent among athletes. All types of iron deficiency may affect physical performance and should be treated. The main mechanisms by which sport leads to iron deficiency are an increased iron demand, an elevated iron loss and a blockage of iron absorption due to hepcidin bursts. As a baseline set of blood tests, haemoglobin, haematocrit, mean cellular volume (MCV), mean cellular haemoglobin (MCH) and serum ferritin levels are the important parameters to monitor iron deficiency. In healthy male and female athletes >15 years, ferritin values <15µg/l are equivalent to empty, values from 15 to 30µg/l to low iron stores. Therefore a cut-off of 30µg/l is appropriate.