Urinary tract infections are relatively common in pregnancy and may result in significant morbidity for the pregnant woman and fetus. The authors recommend that all pregnant women be screened for the presence of bacteriuria at their first prenatal visit. Failure to treat bacteriuria during pregnancy may result in as many as 25% of women experiencing acute pyelonephritis. Women with acute pyelonephritis may sustain significant complications, such as preterm labor, transient renal failure, ARDS, sepsis and shock, and hematologic abnormalities. Pregnant women with urinary tract infections should be followed up closely after treatment because as many as one third will experience a recurrence.