The risk of cancer after diagnostic X-rays received as fetus or during early childhood has been investigated in many studies. The results of recent epidemiological studies are summarized in a present systematic review. The strategies for literature search, inclusion criteria, and items for study quality assessment were defined in the study protocol. All epidemiological case control and cohort studies published in English between 1990 and 2006 that reported at least the size of the study population and risk estimates were included. Results were summarized separately for pre- and postnatal exposure and for each cancer site. Nineteen case control studies and six cohort studies matched the inclusion criteria. No association of leukemia with prenatal exposures was observed in nine case control studies. Heterogeneous results were found for postnatal exposures and leukemia in four studies. No significant effect of pre- and postnatal X-ray exposure was observed for other cancer sites (non-Hodgkin lymphomas, solid tumors and brain tumors). Most studies have limitations in study design, study size, or exposure measurement, and involve very low exposures. These results thus do not contradict previous evidence accumulated since 1956 indicating risk increases associated with prenatal X-ray exposure. Computed tomography is not covered in the studies and needs to be investigated in the future.