During the past 25 y numerous studies have been performed in infants and children to determine whether environmental exposure to polychlorinated biphenyls (PCBs), dibenzo-p-dioxins, dibenzofurans (PCDFs) and dichlorodiphenyl trichloroethane is causally associated with neurobehavioral effects. In addition, 1 episode of poisoning with PCDFs occurred in Taiwan in 1978. This poisoning outbreak is referred to as Yu-Cheng, oil disease, since the PCDFs and PCBs had accidentally contaminated cooking oil. In the aggregate the studies reviewed here show no conclusive evidence that environmental exposure to these chemicals affect the neurobehavioral development of infants and children.