In this case report, a germ line genome project identified a pathogenic variant in TP53 in a three-year-old girl diagnosed with rhabdomyosarcoma. The variant causes the cancer predisposition syndrome Li-Fraumeni syndrome (LFS). The girl's family was genetically counselled, and the same variant was identified in her mother and sister. The family was afterwards offered surveillance according to national guidelines. With this report, we want to focus on cancer predisposition syndromes and to discuss the benefits regarding surveillance of children with LFS.