A routine urine culture was performed in 1130 normal pregnant women and in 211 high-risk pregnancies (136 diabetics and 75 women with a previous urinary tract infection). Asymptomatic bacteriuria was found in 5.9% of the normal pregnancies, 12.5% among the diabetics and in 18.5% of the previous urinary tract infection patients. The higher incidence of a clinical urinary tract infection among patients with asymptomatic bacteriuria was found statistically significant (p less than 0.001) in all three groups. A high correlation was found between a negative urine culture in early pregnancy and the absence of development of cystitis and pyelonephritis in later pregnancy. The incidence of asymptomatic bacteriuria in normal pregnant women who developed cystitis later in pregnancy was 33.3% and in those developing pyelonephritis, 66%. In the two high-risk pregnancy groups, the incidence of asymptomatic bacteriuria among those developing clinical infection was even higher, 58.3 and 85.7%, respectively, among the diabetics, and 60 and 66.6% respectively, among the previous urinary tract infection patients.