A prisoner sliced off his penis with a razor blade smuggled into his cell, according to reports.
Guards raised the alarm when the convict was found covered in blood and in agony, and he was raced by paramedics to a hospital that specialises in "traumatic limb reattachment".
Prison staff were horrified after finding the badly injured man during a shift change at the Montgomery County Correctional Facility in Boyds, Maryland, in the US.
It was unclear why the man sliced off his penis and whether surgeons were able to successfully reattach it.
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One report claimed the inmate has mental health problems.
Sources told local TV station WJLA that the prisoner cut off his own penis using a blade smuggled into his cell.
Guards found him during a shift change at 3pm last Saturday.
Reporter Kevin Lewis tweeted: "Sources tell me an inmate at the Montgomery County Correctional Facility used a razor to cut off his penis yesterday.
"Paramedics took the man to a hospital that specializes in 'traumatic limb reattachment.'
"The grisly discovery left jail staff horrified."
The man was booked into the jail in February for assault and resisting arrest, WJLA reported.
An investigation is under way to discover how the prisoner managed to obtain the razor blade.
According to its website, the Montgomery County Correction Facility holds male and female offenders who are awaiting trial or serving sentences of up to 18 months.
It has a capacity for 1,028 inmates.
