Influenza virus infection complicating pregnancy remains a matter of concern because of the frequency of these infections and possible associated increased maternal and perinatal risks. Influenza A/Bangkok (H3N2) infection occurred in a gravid woman in association with fever, chills, and uterine tenderness and contractions together with maternal and fetal tachycardia. Initial evaluations led to consideration of amniotic fluid infection syndrome with planned termination of the pregnancy. Examination of amniotic fluid obtained by amniocentesis showed neither microorganisms nor neutrophils, and close monitoring and supportive measures were continued. Amniotic fluid and maternal nasopharyngeal washing both yielded influenza A/Bangkok (H3N2). Mother and fetus were closely monitored until term. Cord blood samples demonstrated hemagglutination inhibition and complement fixation antibody titers of 1:32 and greater than 1:512, respectively. Cord blood IgM and IgA hemagglutination inhibition antibody concentrations were 6,400 and 3,200 micrograms/ml, respectively, consistent with transplacental infection. This is the first confirmation of transplacental influenza infection. This generally self-limited viral infection may mimic the amniotic fluid infection syndrome and put mother and fetus at risk for potentially harmful untimely delivery.