Maternal illness during pregnancy is not uncommon and sometimes requires radiographic imaging for proper diagnosis and treatment. The patient and her physician may be concerned about potential harm to the fetus from radiation exposure. In reality, however, the risks to the developing fetus are quite small. The accepted cumulative dose of ionizing radiation during pregnancy is 5 rad, and Mo single diagnostic study exceeds this maximum. For example, the amount of exposure to the fetus from a two-view chest x-ray of the mother is only 0.00007 rad. The most sensitive time period for central nervous system teratogenesis is between 10 and 17 weeks of gestation. Nonurgent radiologic testing should be avoided during this time. Rare consequences of prenatal radiation exposure include a slight increase in the incidence of childhood leukemia and, possibly, a very small change in the frequency of genetic mutations. Such exposure is not an indication for pregnancy termination. Appropriate counseling of patients before radiologic studies are performed is critical.