Over the past 50 years, our laboratory has provided consultations dealing with the risks of various environmental toxicant exposures during pregnancy. These contacts were primarily by telephone or written communications. Since the year 2000, the primary source of consultations has been via the internet. In 2007, the pregnancy website of the Health Physics Society received 1,299,672 visits. The contacts who downloaded information totaled 620,035. After reading the website information, 1442 individuals who were still concerned contacted me directly. Unfortunately, we have learned that many physicians and other counselors are not prepared to counsel patients concerning radiation risks. Approximately, 8% of the website contacts, who had consulted a professional, were provided inaccurate information that could have resulted in an unnecessary interruption of a wanted pregnancy. Research from our and other investigators' laboratories has provided radiation risk data that are the basis for properly counseling contacts with radiation exposures. Mammalian animal research has been an important source of information that improves the quality and accuracy of estimating the reproductive and developmental risks of ionizing radiation in humans. What are the reproductive and developmental risks of in utero ionizing radiation exposure? 1. Birth defects, mental retardation, and other neurobehavioral effects, growth retardation, and embryonic death are deterministic effects (threshold effects). This indicates that these effects have a no adverse effect level (NOAEL). Almost all diagnostic radiological procedures provide exposures that are below the NOAEL for these developmental effects. 2. For the embryo to be deleteriously affected by ionizing radiation when the mother is exposed to a diagnostic study, the embryo has to be exposed above the NOAEL to increase the risk of deterministic effects. This rarely happens when the pregnant women have x-ray studies of the head, neck, chest or extremities. 3. During the preimplantation and preorganogenesis stages of embryonic development, the embryo is least likely to be malformed by the effects of ionizing radiation because the cells of the very young embryo are omnipotential and can replace adjacent cells that have been deleteriously affected. This early period of development has been designated as "the all-or-none period." 4. Protraction and fractionation of exposures of ionizing radiation to the embryo decrease the magnitude of the deleterious effects of deterministic effects. 5. The increased risk of cancer following high exposures to ionizing radiation exposure to adult populations has been demonstrated in the atomic bomb survivor population. Radiation-induced carcinogenesis is assumed to be a stochastic effect (nonthreshold effect) so that there is theoretically a risk at low exposures. Whereas there is no question that high exposures of ionizing radiation can increase the risk of cancer, the magnitude of the risk of cancer from embryonic exposures following diagnostic radiological procedures is very controversial. Recent publications and analyses indicate that the risk is lower for the irradiated embryo than the irradiated child, which surprised many scientists interested in this subject, and that there may be no increased carcinogenic risk from diagnostic radiological studies. Examples of appropriate and inappropriate counseling will be presented to demonstrate how counseling can save lives and change family histories. The reader is referred to the Health Physics Society website to obtain many examples of the answers to questions posed by women and men who have been exposed to radiation (www.hps.org). Then click on ATE (ask the expert).