Kidney failure has traditionally been categorised as mild, moderate or severe. Other poorly defined terms like uraemia and end-stage kidney disease have commonly been applied. During the last few years, an international consensus has emerged staging chronic kidney disease into 5 stages: stage 1 being glomerular filtration rate (GFR) > 90 ml/min and signs of kidney damage, stage 2 GFR 60-89 ml/min and signs of kidney damage, stage 3 being GFR 30-59 ml/min, stage 4 being GFR 15-29 ml/min, and stage 5 GFR < 15 ml/min. Kidney function should be calculated from creatinine-based formulas, or measured by isotope or iohexol clearances rather than as renal clearance of creatinine in timed urine samples. We address the importance and implications of these new definitions.