Estimates of the prevalence of sexual activity in prison vary although it is accepted that consensual sex is part of prison life. Some surveys estimate the number of prisoners engaging in sexual activity to be as low as 3%; others suggest it is as high as 30%.

Strang reported that 21 men (2%) admitted having sex with another man while in prison. Three reported their first homosexual contact in prison. Four admitted having regular a regular sex partner in prison at the time of the interview, but only one reported using condoms. Five men, none of who reported using condoms, admitted having been paid to have sex with men in prison: numbers of partners ranged from 1 to 50. Edwards found that 2/378 (0.53%) admitted having sex with a male partner in prison. A study conducted in 1997 and 1998 by the Public Health Laboratory Service found that 3% of male prisoners reported having had sex with another man while in prison.

Accurate figures are difficult to collect due to the stigmatising of (mainly) homosexual activity in prison, but research suggests that sexual activity is more common in prisons holding those serving longer sentences. Coercive sexual activity is anecdotally common although considerably under-reported.

One of the few investigations on this issue, The Howard Journal of Criminal Justice study of May 2004 (Banbury) reported that a survey of ex-prisoners found that one per cent - around 2 000 men- had experienced forced penetrative sex attacks out of the 200,000 who pass through the prison system annually.

Transmission of HIV (and other sexually transmitted infections) may occur through unprotected penetrative sex between men. Many of the men having sex with other men in prisons define themselves as heterosexual, and they may falsely believe they are not at risk. Additionally, they are likely to return to other sexual partners on release, with neither person being aware of any risk.