**1. Introduction**

Indexing glomerular filtration rate (GFR) for body surface area (BSA) is routine practice, but criticism has been raised on indexing GFR for BSA in children, obese and anorectic patients. Over the years other ways of indexing GFR have been proposed, including height, lean body mass, body weight, ideal weight, plasma volume, total body water and especially extracellular volume (ECV). Based on a literature review and on statistical analyses of GFR data of children, we consider the following main questions: Why do we normalize GFR for BSA? Is it really necessary to index GFR? And if so, are there other or better ways to normalize GFR?
