The effective radiation doses received by children living in high radon areas are similar to those which have been associated with an excess risk of malignant disease elsewhere. However, the only cancer known to be associated with radon is lung cancer--a disease which is not a condition of childhood. Thorne and his colleagues have conducted a study which could have demonstrated an excess of childhood malignancy only if the risk associated with radon was very high. The risk to health of high levels of radon in the environment remains uncertain. The United Kingdom Case Control Study of Childhood Cancers, under the chairmanship of Sir Richard Doll, is assessing risk from many factors including measured radon exposure and it is with great interest that we await the results.