Zika virus (ZIKV) infection during pregnancy can cause fetal brain injury without microcephaly, and this injury can be difficult to detect, new research shows. Researchers inoculated five pregnant pigtail macaques with ZIKV and studied the effects on their fetuses. Weekly ultrasound imaging revealed no obvious abnormality in four of the five fetuses, and none met the criteria for microcephaly. Nevertheless, MRI revealed T2-hyperintense foci in four of the five fetuses and abnormally low ratios of noncortical tissue to total brain volume after 100 days of gestation. Pathological analysis showed that ZIKV reduced late fetal neurogenesis, raising the possibility that impairment of neurogenesis could cause cognitive impairments into adulthood in individuals who were exposed to ZIKV during gestation but did not develop microcephaly. Long-term monitoring of such individuals is therefore recommended.