Accurately estimating the glomerular filtration rate (GFR) is unfortunately not an easy task. Multiple methods for doing this have been developed over the past few decades and each newly adopted method, although better than its predecessor, has been far from perfect. The method currently in vogue, the MDRD equation, is no exception. MDRD GFRs are only rough approximations. This is important to remember when assessing a patient and when trying to explain to them the status of their kidney disease.