The detrimental effects of cigarette smoking on the kidney in healthy individuals without established renal diseases have not been established. We evaluated the effects of smoking on renal function and proteinuria in 35 288 apparently healthy participants who were not on antihypertensive and/or antidiabetic medication and who had undergone a health examination at the Health Promotion Center, Seoul National University Hospital from 1995 to 2006. Renal function was estimated using the simplified Modification of Diet in Renal Disease Study equation for estimated glomerular filtration rate (eGFR), and proteinuria was determined by the spot urine dipstick test. Adjusted eGFR was higher in current smokers (mean+/-s.e.m., 79.3+/-0.1 ml min(-1)) than in ex-smokers (77.3+/-0.2 ml min(-1), P<0.001) and non-smokers (77.7+/-0.1 ml min(-1), P<0.001). The adjusted eGFR of smokers who smoked >20 cigarettes per day were higher than that of individuals who smoked < or =20 cigarettes per day (P<0.001). In participants with an eGFR of <50 ml min(-1), current smoking (38.3+/-1.9 ml min(-1)) and past smoking (39.5+/-1.9 ml min(-1)) were associated with significantly lower eGFR values than non-smoking (45.1+/-1.2 ml min(-1); P=0.007 and P=0.027, respectively). Current smoking was associated with a higher risk of proteinuria (urine dipstick for albuminuria > or =1+) than non-smoking (odds ratio=1.380, P<0.001). In conclusion, cigarette smoking is associated with a higher eGFR in the general population, whereas it might reduce eGFR in a small subset of the population and increase the risk of proteinuria. These subsets should be better defined to prevent chronic kidney diseases related to smoking in the general population.