As patients with impaired kidney function are at increased risk not only for progressive renal function loss, but also for cardiovascular disease, it is of importance to have accurate techniques to screen patients for the presence of an impaired kidney function. Glomerular filtration rate can in mass screenings best be evaluated using a formula based upon a serum creatinine measurement and anthropometric parameters. The Cockcroft-Gault and Modification of Diet in Renal Disease (MDRD) formulas are mostly used. Both are easy to use, but have their limitations. Interpreting the results of such glomerular filtration rate estimates requires a good knowledge of these limitations. Urinary albumin excretion can best be measured from 24 h urine collections. As these collections are difficult to perform, however, an early morning spot urine sample for the measurement of urinary albumin concentration can be applied as preselection for screening purposes. Mass screening for early kidney function impairment, expressed by an impaired glomerular filtration rate or elevated urinary albumin excretion, may help to detect patients at increased cardiac and renal risk. This can best be done using formulas to estimate glomerular filtration rate and by measuring urinary albumin loss.