The red cell distribution width (RDW) is a measure of the variation in the size of erythrocytes. It is widely used to differentiate types of anaemia. Moreover, the association of RDW with inflammatory biomarkers has been demonstrated. Recently, RDW has been proven to be a strong predictor of cardiovascular disease. Further, a strong correlation between RDW and the severity of liver cirrhosis has been shown, and also, there are observations showing the importance of RDW in pulmonary and renal diseases, diabetes, inflammatory bowel disease and coeliac disease. However, most of the previous studies were conducted on adults but this fact may be instrumental in motivating similar studies to be conducted on children in the future.