The number of serious complaints made by prisoners in Castlerea Prison increased by 60% last year.
According to figures released under the Freedom of Information Act, prisoners in Castlerea made 15 serious complaints in 2018 - up from 9 in 2017.
The data shows no category A complaint has been made by inmates in Castlerea so far this year.
Nationally, the number of serious complaints from prisoners increased from 70 in 2017 to 80 last year, while 42 complaints were lodged in the first seven months of this year, including allegations of assaults and sexual and racial abuse.
But since the beginning of 2017, only 16 complaints have been upheld or partly upheld.
Gabriel Keaveny, assistant general-secretary of the Prison Officers Association, says there's a serious problem with false allegations, and vexatious complaints should be punished....