We have reviewed the evidence for CHEK2 as a cause of Li–Fraumeni syndrome (LFS) in view of the continued debate about the cancer spectrum associated with mutations in this gene.1 In 1969 Li and Fraumeni reported four families with an autosomal dominant predisposition to a range of cancer types in children and young adults, including soft tissue sarcoma and breast cancer.2 In 1988, they extended their analysis to 24 families to characterise better the phenotype of the syndrome.3 These families contained greater than expected numbers of soft tissue sarcomas, osteosarcomas, breast cancers, childhood adrenocortical carcinomas, brain tumours and leukaemia. This group of cancers was soon accepted as the formal criteria for the clinical definition of classical LFS (box 1).