Twenty-five patients with squamous cell carcinoma (SCC) of the anus have presented over an 8 year period; 18 were female. Six of 9 patients aged under 50 years were female. Five of these women had been treated for a previous cervical malignancy (2 invasive) and 4 practised anal intercourse; human papillomavirus (HPV) type 16 DNAs were isolated from their arcival anal/cervical paraffin sections. Signals were confined to the nuclei of the invasive anal SCC cells and the transformation zone of the cervix. HPV 6, 11 and 18 DNAs were not identified. Young women with cervical intraepithelial (CIN) III or invasive cervical SCC found in association with HPV infection are at risk of developing anal SCC (P less than 0.001; Fisher's exact).