Microalbuminuria is a strong and independent indicator of increased cardiovascular risk among individuals with and without diabetes. Therefore, microalbuminuria can be used for stratification of risk for cardiovascular disease. Once microalbuminuria is present, cardiovascular risk factor reduction should be more "aggressive." The nature of the link between microalbuminuria and cardiovascular risk, however, remains poorly understood. There is no strong evidence that microalbuminuria causes atherothrombosis or that atherothrombosis causes microalbuminuria. Many studies have tested the hypothesis that a common risk factor underlies the association between microalbuminuria and cardiovascular disease but, again, have found no strong evidence in favor of this contention. At present, the most likely possibility is that a common pathophysiologic process, such as endothelial dysfunction, chronic low-grade inflammation, or increased transvascular leakage of macromolecules, underlies the association between microalbuminuria and cardiovascular disease, but more and prospective studies of these hypotheses are needed.