['Increasing evidence suggests an association between oestrogens and colorectal cancer. Oestrogen receptor beta, ER-β, putatively plays a pathobiological role in colorectal cancer as colorectal epithelial cells frequently express ER-β. The aim was to elucidate the association of the dinucleotide (CA) repeat polymorphism of the ER-β gene (ESR2) with colorectal cancer.', '\u2002Deoxyribonucleic acids extracted from the renal cortex of 1488 Japanese autopsies with complete clinical/pathological data were studied. CA repeat polymorphism was determined by polymerase chain reaction using fluorescein-labelled primers. Patients were divided into three genotype groups according to the number of CA repeats of each allele (S\u2003<\u200322, L ≥\u200322); SS (with two S alleles), SL (with one each S and L allele) and LL (with two L alleles). The presence/absence of colorectal cancers was determined by examining the clinical records and autopsy material. The incidence of colorectal cancer was significantly different according to the ESR2 CA repeat genotype only among females (SS, 37/202\u2003=\u200318.3%; SL, 19/332\u2003= 5.7%; LL, 5/155\u2003=\u20033.2%, P\u2003<\u20030.0001). Immunohistochemically, cancers in females with the SS genotype, but not the SL genotype, frequently expressed the C-terminus portion of ER-β1 (wild-type ER-β).'] Is oestrogen receptor-β CA repeat polymorphism associated with incidence of colorectal cancer among females?