Seventy complaints were made last year by prisoners alleging assault, excessive force, racial abuse, ill-treatment, discrimination or intimidation.
More than a third of them came from a single prison, the Midlands Jail in Co Laois, from where there were 25 individual complaints logged.
Of the 70 complaints made, just a single one has so far been upheld while one was considered to have been “vexatious”.
Twenty six of the complaints were not upheld, two were withdrawn, while the majority of them are incomplete and still under investigation.
The Irish Prison Service has admitted they are concerned about long delays in dealing with the most serious of complaints made by the incarcerated.
They said this was down to a shortage of suitably qualified investigators as well as a backlog built up during the Covid-19 pandemic when prisoners could not always be interviewed face-to-face.
The seventy ‘Category A’ complaints were among a total of 1,045 made by inmates in the Irish prison system last year, according to records released under FOI.