Objectives: This study was undertaken to determine the incidence of asymptomatic bacteriuria(ASB) during pregnancy and itsprevalance in the three trimesters. Subjects and Methods: One hundred and ten pregnant women in their first trimester attending the antenatal outpatient clinic withno urinary tract complaints were included in the study. After perineal cleaning, urine samples were obtained from all patients forculture and microscopic evaluation. Approximately 1 mL urine was sampled using the midstream catch technique. Patients with bacterial counts over 100,000 with the midstream catch technique were considered to have asymptomatic bacteriuria. Patients fuliling the criteria for bacteriuria were treated with either penicillin or cephalosporine for one week, depending on the in vitro sensitivity test results. Results: ASB rate in the study group was 8.1%. E. coli was isolated as the pathogenic organism in 77.77% of the cases with ASB.ASB was found to be more frequent in patients over age 25 and the average age of pregnant women with ASB was 29.89 ± 5.80 (p < 0.05). Average duration of gestation in the group with ASB was 28.11 ± 2.26 weeks. ASB rate in the group age 35 and over was 22.22% (p < 0.05). ASB was diagnosed in nine patients; one of these patients was in the first trimester, two were in the second trimester, and six in the third trimester. Clustering in the third trimester was found to be statistically significant (p < 0.05). Conclusion: ASB distribution in the first, second, and third trimesters was 0.9%, 1.83%, and 5.6%, respectively. There was a significant relationship between advanced maternal age and incidence of ASB. Women with no bacteriuria in their initial examination in the first trimester developed bacteriuria in the later trimesters. We, therefore, suggest that it would be prudent to screen pregnant women for bacteriuria in the second and third trimesters.