The authors present literature review of usefulness of serum creatinine concentration measurements in comparison with cystatin C concentration for assessment renal function in chronic kidney disease and concomitant diseases. In this article different methods of determining renal filtration are critically discussed. In comparison with creatinine, cystatin C is a good parameter for assessing stable renal function and their early damage. It is a marker of subclinical disorders in chronic renal failure which is also useful in assessing renal dysfunction in coexisting diseases. Cystatin C is more precise than creatinine especially in pediatric, elderly, diabetic and oncological patients. It is more accurate because it is not associated with amount of muscle mass and nutritional status. Among many parameters cystatin C is a promising marker broadening diagnostic tools in nephrology.