The Department of Corrections released the data to RNZ under the Official Information Act, following the sentencing of Stephen Mark Gotty for a sex attack.
Gotty, a repeat sex offender, was allowed to choose his cellmate, and he sexually attacked the 19-year-old once their cell door was locked on their first night.
According to Corrections, 15 prisoners subject to double-bunking have complained of being sexually assaulted by their cellmate, in or outside their cell, from 2010 to 2016.