Cystatin C, an endogenous low-molecular-weight marker of glomerular filtration rate, has recently been shown to be associated with future cardiovascular disease in healthy elderly populations and patients with documented atherosclerosis in a dose-dependent manner that possibly reflects a very early stage of chronic renal dysfunction. At the same time, local cystatin C deficiency has been demonstrated in atherosclerotic and aneurismal lesions, suggesting a protective role of cystatin C in the vessel wall, possibly in concert with TGF-beta1. Although cystatin C is not an acute phase reactant, large epidemiological studies have documented a highly significant association between serum cystatin C and mildly increased C-reactive protein (CRP) levels, the hallmark of the chronic inflammatory state associated with atherosclerosis and chronic renal failure. Since cystatin C is produced by all nucleated cells, it is unlikely that local variations in cystatin C synthesis in diseased arteries--rather than global cystatin C production and renal elimination--should determine its serum concentration. Consequently, the present review proposes microinflammation as the unifying concept for both lines of evidence.