Prison rape is rape occurring in prison. It has come into common usage to refer to rape of inmates by other inmates, and less commonly to the rape of inmates by staff, and even less commonly rape of staff by inmates.
Public awareness of the phenomenon of prison rape is a relatively recent development and estimates of its prevalence have varied widely for decades. In 1974 Carl Weiss and David James Friar wrote that 46 million Americans would one day be incarcerated; of that number, they claimed, 10 million would be raped.
A United States Department of Justice report, Sexual Victimization in Prisons and Jails Reported by Inmates, states that "In 2011-12, an estimated 4.0% of state and federal prison inmates and 3.2% of jail inmates reported experiencing one or more incidents of sexual victimization by another inmate or facility staff in the past 12 months or since admission to the facility, if less than 12 months."  However, advocates dispute the accuracy of the numbers, saying they seem to under-report the real numbers of sexual assaults in prison, especially among juveniles.
A 1992 estimate from the Federal Bureau of Prisons conjectured that between 9 and 20 percent of inmates had been sexually assaulted. Studies in 1982 and 1996 both concluded that the rate was somewhere between 12 and 14 percent. A 1986 study by Daniel Lockwood put the number at around 23 percent for maximum security prisons in New York. In contrast, Christine Saum's 1994 survey of 101 inmates showed 5 had been sexually assaulted.
The Prison Rape Elimination Act of 2003 was the first United States federal law passed specifically dealing with the sexual assault of prisoners. The bill was signed into law on September 4, 2003.