In this study we aimed to find out the frequency of asymptomatic bacteriuria (ASB), relation between bacteriuria and duration of diabetes in patients with diabetes mellitus (DM) prospectively. A total of 100 diabetic patients (75 female, 25 male) who were 19-78 years of age and 100 nondiabetic patients (75 female, 25 male) applying to the Department of Internal Medicine without having urinary tract infection (UTI) symptoms but for reasons other than infection (control subjects) were included. Two clean-catch midstream urine samples of the patients were obtained and cultured for the evaluation of ASB with an interval of twentyfour hours. ASB was defined as the same bacteria growing ≥ 105 colony forming units (cfu) per ml of both urine samples in the absence of UTI symptoms. Frequency of ASB was 26% (30.7% in women, 12.0% in men) in the diabetic patients and 7% (9% in women, 4% in men) in the control group (p< 0.05). Although the difference of ASB between diabetic and nondiabetic women was statistically significant (p< 0.05), it wasn’t sig-nificant between diabetic and nondiabetic men (p> 0.05). It was observed that the frequency of ASB increased significantly by increasing the duration of DM in diabetic patients (p< 0.05). In conclusion, the frequency of ASB in diabetic patients is higher than nondiabetics. For this reason, we think that the diabetic patients who are older and have longer duration of diabetes should be searched for ASB and, in order to decide for ASB treatment, further studies are necessary