A glomerular filtration rate (GFR) <60 ml/min/1.73 m2 is associated with an increased risk of cardiovascular disease and renal insufficiency. The formula of the 'Modification of diet in renal disease' (MDRD) study is derived from plasma-creatinine concentrations and estimates GFR based on age, sex and race. Many clinical laboratories have started to report estimated GFR using this formula, which may lead to earlier recognition of chronic kidney disease. Clinicians should understand for which patients the MDRD formula may be appropriate and be aware of its limitations.