Summary. In clinical practice, serum creatinine is most commonly used to estimate glomerular filtration rate (GF) although it is well known that serum creatinine may be influenced by GF and factors independent of GF (age, sex, race, body size, diet, certain drugs and analytical methods). Creatinine clearance is a more sensitive marker of GF, but it overestimates GF because of tubular secretion of creatinine, and it often involves errors in 24-hour urine collection. According to the NKF/ KDOQI (National Kidney Foundation Kidney Disease Outcome Quality Initiative) guidelines, the level of GF should be estimated from prediction equations taking into accout serum creatinine concentration and demographic characteristics. The aim of this work is to emphasize the clinical usefulness of these equations in estimating GF. Using prediction equations to estimate GF does not require timed urine collection susceptible to errors which are the most common underlying cause of unreliable estimation of GF done by creatinine clearance.