We describe the epidemic of microcephaly in Brazil, its detection and attempts to control it, the suspected causal link with Zika virus infection during pregnancy, and possible scenarios for the future. In October 2015, in Pernambuco, Brazil, an increase in the number of newborns with microcephaly was reported. Mothers of the affected newborns reported rashes during pregnancy and no exposure to other potentially teratogenic agents. Women delivering in October would have been in the first trimester of pregnancy during the peak of a Zika epidemic in March. By the end of 2015, 4180 cases of suspected microcephaly had been reported. Zika spread to other American countries and, in February 2016, the World Health Organization declared the Zika epidemic a public health emergency of international concern. This unprecedented situation underscores the urgent need to establish the evidence of congenital infection risk by gestational week and accrue knowledge. There is an urgent call for a Zika vaccine, better diagnostic tests, effective treatment, and improved mosquito-control methods.