Her Majesty's Young Offender Institution (or HMYOI) is a type of British prison intended for offenders aged between 18 and 21. There are as of 2005 14 dedicated institutions: In 2007 young offender institutions will be abolished with those over 18 sent to adult prisons.

• HMP Ashfield
• HMYOI Aylesbury
• HMYOI Deerbolt
• HMYOI Huntercombe
• HMYOI Lancaster Farms
• HMYOI Northallerton
• HMYOI Onley
• HMYOI Polmont
• HMYOI Portland
• HMYOI Rochester
• HMYOI Stoke Heath
• HMYOI Swinfen Hall
• HMYOI Thorn Cross
• HMYOI Werrington
• HMYOI Wetherby

and 20 which share their site with other penal establishments:

• HMP & YOI Askham Grange
• HMP & YOI Brinsford
• HMP & YOI Brockhill
• HMP & YOI Bullwood Hall
• HMP & YOI Castington
• HMP & YOI Chelmsford
• HMP & YOI Durham
• HMP & YOI East Sutton Park
• HMP & YOI Feltham
• HMP & YOI Guys Marsh
• HMP & YOI Hindley
• HMP & YOI Hollesley Bay
• HMP & YOI Low Newton
• HMP & YOI Moorland
• HMP & YOI New Hall
• HMP & YOI Norwich
• HMP & YOI Reading
• HMP & YOI Warren Hill
• HMP/RC & YOI Exeter
• HMYOI & RC Glen Parva

See Young Offender Institution, Her Majesty's Prison Service