Modern medicine is unimaginable without radiologic diagnostic methods, which offer us quick and noninvasive looks inside the human body. But, from the beginnig of radiology development people started to comprehend the negative effects ionizing radiation has on living organisms. On that ground, nowadays we take a lot of care to use ionizing diagnostic methods rationally, especially concerning pregnant women. The embryo, and later fetus, is more radiosensitive than a grownup, due to the higher rate of cell proliferation and metabolic activity. Organogenesis, lasting from the 3rd to the 8th weeks of gestation, is a period of human development during which the embryo is the most susceptible to impacts of ionizing radiation. If the fetal dose of radiation during this time interval exceeds 100 mGy, there is an increased risk of fetal anomalies. It is also believed that there is a risk of carcinogenic effects throughout the whole pregnancy, associated with fetal doses above 10 mGy. These effects are later seen as an added risk of childhood leukemia. The fetal dose almost never exceeds 50 mGy in ionizing radiologic examinations, and is much lower in most of them. The American College of Obstetricians and Gynecologists claims that a fetal dose of <50 mGy is not harmful for the fetus and that a single ionizing examination during pregnancy does not pose any additional risk of fetal anomalies. Even though nonionizing diagnostic methods (ultrasound, MR) are methods of first choice in pregnant women, there are situations when the use of ionizing methods is necessary. In such cases, the risk associated with the illness or condition of the mother far outweighs the risk of ionizing radiation exposure of the fetus. Avoiding ionizing diagnostic methods out of fear that they will harm the fetus is usually unfounded and delay in diagnosis can harm both the mother and the fetus. Whenever there is a possibility, the dose of ionizing radiation exposure should be reduced and measures of protection should be taken. It is also very important to counsel every pregnant woman undergoing ionizing examination in order to prevent unnecessary termination of a healthy pregnancy.