THE Prisoner Ombudsman is to investigate the death in custody of a 27-year-old man.
The Prison Service confirmed that the man, who had been in the medium security Magilligan jail, died in hospital on Monday.
It said his family have been informed and as is standard procedure, the PSNI, Coroner and Prisoner Ombudsman have launched investigations into the death.
The man's death brings the total number of people to die in prison in Northern Ireland since 2007 to 53.
Four prisoners died last year.
Ronnie Armour, director general of the Prison Service, said he wanted to extend sympathy to the family of the prisoner.
"My thoughts are with them at this difficult time," he said.