Analysis of data from the Kanto-Ko-Shin-Etsu Branch of the Japan Children's Cancer Registry revealed that mass screening for neuroblastoma increased the detection of cases in infants younger than 1 year from about 25% before screening to about 50%, and the percentage of neuroblastomas among all pediatric cancers almost doubled, from approximately 10% to 19.3%. However, when the cases found on screening were subtracted, the numbers after the onset of mass screening were similar to those before screening. It is likely that neuroblastoma mass screening has identified a unique type of tumor, which may not be recognized without mass screening, rather than that it has contributed to the earlier diagnosis of tumors in older children.