[en] Patient dose assessment during medical exposure in paediatric diagnostic radiology is of highest importance in view of the greater radiation hazard to children compared to adults. It is conditioned by their higher sensitivity to ionizing radiation and their greater life expectancy. The risk of stochastic effects is several times greater for children than for adults. The attributive risk to children exposed to ionizing radiation during the first 10 years is 3 to 5 times greater than the risk to adults exposed between 30 and 40 years of age, and 6 to 7 times greater compared to the risk to adults exposed after their 50 year. The children dose distribution studies are carried out in order to elaborate national diagnostic reference levels. The dose assessment is complicated by the great variation in body size and anatomical features of children belonging to different age groups. There is a series of difficulties in the definition of image quality criteria and guidelines for good practice due to the dynamically changing body proportions and the anatomical features as a result of the active growth process from infancy through early childhood to adolescence. (author)