Infections acquired in utero or during the birth process are a significant cause of fetal and neonatal mortality and an important contributor to early and later childhood morbidity. Advances in ultrasound, invasive prenatal procedures and molecular diagnostics have allowed in utero evaluation and given rise to more timely and accurate diagnosis in infected fetuses. Transplacental transmission of the infectious agent, even in subclinical maternal infection, may result in a severe congenital syndrome. Prenatal detection of infection is based on fetal sonographic findings and polymerase chain reaction to identify the specific agent. Nevertheless, most affected fetuses appear sonographically normal, but serial scanning may reveal evolving findings. Sonographic fetal abnormalities may be indicative of fetal infections, although they are generally not sensitive or specific. These include growth restriction, hydrops, ventriculomegaly, hydrocephaly, microcephaly, intracranial or hepatic calcifications, ascites, hepatosplenomegaly, echogenic bowel, placentomegaly, and abnormal amniotic fluid volume. When abnormalities are detected on ultrasound, a thorough fetal evaluation is recommended because of potential multiorgan involvement. The sonologist should understand the limitations of ultrasound. Patients should be counseled that ultrasound is not a sensitive test for fetal infection and that a normal fetal anatomy survey cannot reliably predict a favorable outcome.