Urinary tract infections (asymptomatic bacteriuria, cystitis, and pyelonephritis) are frequently encountered medical complications of pregnancy. The majority of infections in pregnancy are asymptomatic; however, even covert bacteriuria places the mother at risk for low birth weight and preterm birth. Pyelonephritis can result in significant maternal and fetal morbidity and mortality. Therefore, all pregnant women should be screened for asymptomatic bacteriuria, and urinary tract infections should be promptly treated to prevent adverse pregnancy outcome. This article reviews the diagnosis, etiology, treatment, and complications associated with urinary tract infections in pregnancy.