This final report updates preliminary data on Zika virus infection among pregnant women in Rio de Janeiro. ZIKV infection during pregnancy was associated with fetal death, fetal growth restriction, and central nervous system abnormalities. We have been conducting active surveillance for dengue infection in the general population of Rio de Janeiro since 2007. In 2012, we established a prospective cohort for dengue surveillance in mother–infant pairs within the Manguinhos Rio de Janeiro area. In 2015, we noted an increase in cases of a denguelike illness that was characterized by a descending rash, generally without fever; this increase coincided with a surge in the number of cases of illness characterized by a pruriginous rash in northeastern Brazil. 1 In early 2015, most cases were originally reported to surveillance systems as dengue; however, Zika virus (ZIKV) was . . .