Cystatin C belongs to the cystatin superfamily, is a potent inhibitor of lysosomal proteinases and probably one of the most important extracellular inhibitors of cysteine protease. It is found in virtually all tissues and body fluids fluids, including plasma, urine and cerebrospinal fluid. Cystatin C is involved in several disease processes through its regulation of cysteine protease activity. Cystatin C is mainly used as a biomarker of kidney function. Recently, it has been studied for its role in predicting new-onset or deteriorating cardiovascular disease. It also seems to play a role in brain disorders involving amyloid, such as Alzheimer’s disease.