Using pedigrees at the Regional Oncogenetic Clinic at Lund University Hospital, the prevalence of childhood cancer was estimated in families with mutations in the BRCA1 (n=98), BRCA2 (n=43) MMR (MLH1, MSH2 MSH6) (n=31) and CDKN2A (n=15) genes in comparison with population based control families (n=854).