Excretion of albumin in the urine is highly variable, ranging from nondetectable quantities to milligrams of albumin and even grams of albumin. Microalbuminuria is defined as low levels of urinary albumin excretion of 30 to 300 mg/d. Microalbuminuria is highly prevalent; in hypertensive and diabetic populations, its prevalence varies from 10 to 40%. It is interesting that microalbuminuria also is found frequently in seemingly healthy individuals (5 to 7%). The variable excretion of albumin in the urine is related to the risk for the individual to develop cardiovascular (CV) disease: Absence or very low levels of albuminuria is associated with low CV risk, whereas the CV risk increases markedly with increasing amount of albumin in the urine (even within the now considered normal range). The predictive power of urinary albumin levels for CV risk is independent of other CV risk factors and not only is present in individual with diabetes and/or hypertension but also in healthy individuals. Treatments that lower albuminuria are associated with CV protection, as demonstrated in randomized, controlled trials of patients with diabetes as well as in patients with hypertension. There is preliminary evidence that albuminuria lowering is CV protective in healthy individuals with an elevated albumin excretion rate. Differences between individuals in their level of albumin excretion are already observed at a very early age (just after birth). In fact, the interindividual variability seems to be relatively constant in the first 5 decades of life, indicating that microalbuminuria is not necessarily a consequence of vascular damage at later age. Higher levels of urinary albumin seem to reflect the ordinary interindividual variability in (renal and systemic) endothelial function. Experimental data show that between strains and even within strains, rats at young age show a remarkable difference in individual endothelial function, and this is strongly related to the susceptibility of that rat to organ damage. In conclusion, albuminuria seems to be a sensitive marker very early in life for the susceptibility of an individual to CV disease. It therefore may be an ideal target for early primary prevention using CV-protective therapy regimens.