Cosmic radiation is an occupational hazard to commercial and military flight crews. Aside from the direct risk to aviators, this ionizing radiation is a hazard to the fetuses of pregnant crewmembers and passengers. Animal studies of low dose ionizing radiation exposures, and human studies following high (lose exposures, suggest that pregnant avia tors may inadvertently subject their fetuses to a risk of decreased cognitive capacity or frank mental retardation, as well as childhood leukemia. Flight attendants sometimes unknowingly exceed recommended maximum cosmic radiation doses to their fetuses, raising social, ethical, and legal issues.