BACKGROUND: Renal function in patients, who undergo medical examination, is usually evaluated by the serum creatinine level. However this numerical value does not always represent the entire renal function because the values increases only when the renal function has decreased more than 50%. The purpose of this study was to find the prevalence of renal diseases through the GFR (Glomerular filtration rate) using MDRD (Modification of Diet in Renal Disease) equation and to analyze the risk factors related to renal diseases. METHODS: We reviewed all the clinical records of 440 patients who had visited for medical examination between January 1, 2004 and December 31, 2004. We have calculated the GFR for each group using the MDRD equation and then figured out the correlation between the GFR and its risk factors. RESULTS: Patients haing GFR of less than 60 mL/min/1.73 m2 were 19 (7.2%), 60~90 mL/min/1.73 m2 were 123 (46.4%) and more than 90 mL/min/1.73 m2 were 123 (46.2%). The correlation between the GFR and age, obesity, hypertension and diabetes melitus were observed as negative results in univariate analysis of variance (P<0.05). Age and diabetes melitus were independent factors affecting the GFR (OR=3.1, 2.2 respectively, P<0.05) in multiple logistic regression analysis. CONCLUSION: It is a well known fact that the declined renal function is related to the aging process and diabetes melitus. Therefore, the mortality rate caused by renal failure and its complications should be decreased through the control of diabetes melitus, aging process and other risk factors.