Anal sex is known to be an important risk factor for anal cancer. Yet compared with vaginal intercourse, little is known about anal sex practices in either heterosexual or male homosexual populations. Of the data that are available, it appears a significant and increasing minority of heterosexuals have ever practised anal intercourse. Among homosexual men, most, but not all, report anal sex, with large proportions of men engaging in both insertive and receptive anal intercourse. The most significant finding of the review was the dearth of population-based data, particularly relating to homosexual men.