A growing body of evidence has been generated indicating that the fetus, infant, and young child are especially susceptible to environmental toxicants as diverse as polycyclic aromatic hydrocarbons (PAHs), pesticides, lead, mercury, polychlorinated biphenyls (PCBs), and environmental tobacco smoke (ETS). Exposures to these toxicants may be related to the increases in recent decades in childhood asthma, cancer, and developmental disability. The Columbia Center for Children's Environmental Health (CCCEH), located in New York City, has developed four cohorts around the world to elucidate the relationships between these exposures and childhood illness. This article summarizes the recent findings from the Center's projects in the context of current research in children's environmental health.