Participants in the CCSS are individuals diagnosed with cancer between 1970 and 1986, before reaching the age of 21. Each participant has been recruited through one of 27 participating clinical research centers, where he or she was diagnosed and/or treated. Study criteria require that all participants must have survived at least five years from their initial diagnosis with cancer; this means that individuals who survived five years and subsequently died are included in the cohort. In addition to cancer survivors, the CCSS has also collected information on a random sample of siblings of survivors. In 2004, survivors in the study ranged in age from 16 to 55 years old.