In pregnancy asymptomatic bacteriuria may cause symptomatic urinary system infections, maternal sepsis, low birth-weight and premature birth, as well as complications such as infrequently preeclampsia, anemia and renal failure. In this study, 224 pregnant women without any complaints of urinary system infection and 48 non-pregnant and sexually active women having no symptom of urinary system infection were included. After the examination of microscopic pyuria, culture was made from mid-stream urine. All cases found positive for pyuria with bacterial growth of 100 000 cfu/mL in urine culture were considered as asymptomatic bacteriuria and the isolation of the same bacteria from the urine cultures of the same cases after 24 hours confirmed the diagnosis. The frequency of asymptomatic bacteriuria was found to be as 6.6% (15/224) and 2.0% (1/48) in pregnant and control groups, respectively. The differences between the two groups were statistically insignificant (p> 0.05). The pregnant with asymptomatic bacteriuria were treated by ampicillin for 7 days. In conclusion, the diagnosis and the treatment of asymptomatic bacteriuria are important to reduce the maternal and newborns' mortality and morbidity rates.