Pyelonephritis is a serious infection in pregnancy and is the consequence of undetected bacteriuria. When the diagnosis of pyelonephritis is made, immediate treatment is mandatory in the hope of preventing the potentially serious maternal and fetal sequelae. After successful treatment, careful surveillance and suppression are required for the remainder of the pregnancy. Moreover, owing to the high incidence of recurrences, both postpartum and during subsequent pregnancies, culture and radiologic investigations are warranted after delivery in an effort to detect underlying renal abnormalities.