In the family reported here, a mother and both of her children developed a Wilms tumour, and all three tumours were of the relatively rare monomorphous epithelial histopathological subtype. Using restriction fragment length polymorphism analysis, both sibs were shown to inherit the same maternal allele from the 11p13 region but different maternal alleles from the 11p15 region. Using a combination of single-strand conformation polymorphism (SSCP) and polymerase chain reaction (PCR) sequencing techniques, no mutations were identified in the WT1 tumour-suppressor gene from the 11p13 region, but a novel polymorphism was identified in exon 1. mRNA expression studies using the insulin-like growth factor II (IGF-II) gene, located in 11p15, showed that there was no relaxation of imprinting at this locus. There was also no evidence of loss of heterozygosity on the long arm of chromosome 16. These findings indicate that the WT1 and IGF-II genes, together with the long arm of chromosome 16, are not directly implicated in tumorigenesis in this Wilms family, but that a recombination event has occurred on the short arm of chromosome 11.