Aim: To determine the most accurate and useful method for calculating creatinine clearance by comparing the results of different methods. Methods: Type 2 Diabetic 100 patients who have been followed by Okmeydani Training and Research Hospital internal medicine and/or diabetes policlinics. Individuals with Type 1 Diabetes Mellitus and acute kidney disease were excluded from the study. Results: Glomerular filtration rate calculated with Cockroft-Gault formula was significantly affected by creatinine, weight and age (p<0.05 for all) in a univariate model. In a multivariate model this was significantly independently affected by creatinine, weight and age (p<0.05 for all). Glomerular filtration rate measured with Modification of Diet in Renal Disease formula was significantly affected by creatinine and age (p<0.05 for all) and in a univariate model. In a multivariate model this was significantly independently affected by creatinine (p<0.05). Glomerular filtration rate measured with 24h urine was significantly affected by creatinine, weight and age (p<0.05 for all). In a multivariate model this was significantly independently affected by weight (p<0.05). Conclusion: In this study, those three methods were similar and positively correlated to each other. Such findings prove that those three different methods are compatible with each other at glomerular filtration calculation and they are all useful in clinical practice. Practical and accurately intensive follow up of those patients will give a chance of better understanding this process and will help us with intervention as soon as possible when needed.