The terms routinely used to describe states of reduced glomerular filtration rate (GFR) not requiring renal replacement therapy are poorly defined. With increasing interest in the epidemiology of chronic renal insufficiency and the timing of initiation of dialysis, terms such as "pre-ESRD" and "pre-dialysis" have been popularized, again without clear definition. Unambiguous terminology should be adopted. The authors favor using the term chronic renal insufficiency to describe states of reduced GFR not severe enough to require dialysis or transplantation. The authors propose classifying patients with GFR of 60 to 41 mL/min, 40 to 21 mL/min, and 20 mL/min or below as having mild, moderate, and advanced degrees of chronic renal insufficiency, respectively. The use of this terminology will facilitate communication among nephrologists and other physicians and provide a framework for comparison of populations across cohort studies and clinical trials.