In patients with diabetes, the development of kidney complications, known as diabetic nephropathy, consist of several stages ending lastly with end stage renal disease. As diabetes mellitus become major devastating disease worldwide so it is important to diagnose its renal complication before it become overt. Glomerular filtration rate (GFR)is a useful index of kidney function. To determine the frequency of subnormal glomerular filtration rate among diabetics who having no other coexistent renal problem depending on the history, clinical examination and investigations including previous renal function tests. Our study conducted on 120 diabetic patients 58 females and 62 males admitted to Basra teaching hospital and Al-Sadder teaching hospital over the period of 6months from June 2009 to January 2010, we excluded the patients with known renal disease, Cockcroft Gault equation have been used to estimate glomerular filtration rate. Stages of chronic kidney disease classification of national kidney foundation was adopted in our study. Among 120 diabetic patients, sex characteristics of the participants were 62 male (51.2%)and 58 female (48.3%), study showed among 120 patients ;45 of them (40.5%) had subnormal GFR (<60ml/min).12 out of the 45 patients with subnormal GFR(9.9%)had too much low GFR that require to initiate the dialysis (<15ml/min).Glomerular filtration rate was higher in male than female which is a normal finding (68.04%versus62.1%).Type 2 diabetes showed lower GFR than type 1(60.57%versus70.28%). Routine measurement of the estimated glomerular filtration rate in the diabetic patients by Cockcroft Gault equation for earlier detection of chronic kidney disease beside other measurement. In our study we support the proposal to include GFR estimation from serum creatinine in the laboratory report as a simple and important tool to diagnose the chronic kidney disease.