INMATE assaults at Northern Ireland's three main prisons have spiked in the past six years - with the number increasing six-fold at one site.
Concerns have been raised about the shocking figures of inmate violence across the Maghaberry, Magilligan and Hydebank jails.
At Maghaberry the number of assaults and fights among prisoners rose six-fold, from 19 in 2009/2010 to 136 in 2014/2015.
During the same period at Magilligan, assaults more than doubled, from 14 to 32 while at Hydebank, there was a 54 percent increase, from 61 to 94.
There was also a significant rise in relation to drugs finds across the three jails.
At Magilligan, the number of drug finds tripled from 51 to 162 while at Maghaberry, the number doubled in the six-year period, from from 168 to 337.
Drug finds also more than doubled at Hydebank, where the figure rose from 131 to 281.
Sinn Fein assembly member Raymond McCartney said the rise in assaults was a "matter of serious concern".
"The length of time prisoners are locked up and not engaged in purposeful activity has also been on the rise and there is no doubt this is a contributory factor in the number of assaults," he said.
"The increase in the number of drugs finds in prisons is also concerning given the serious harm that we know drugs can have. It highlights the need for the Prison Service to address the underlying problem of drug use in prisons here".
SDLP justice spokesman Alban Magennis said the north's prison system was undergoing "serious reform".
"There's good and strong management in place but there needs to be even more effort in terms of taking control of the situation, especially in terms of assaults and injuries and any bullying in the prison complex," he said.
A Prison Service spokesman said "crowding" was recognised as "one the greatest contributing factors" to assaults in prisons.
"In 2010 the average prison population was 1461, in 2014 it was closer to 1800," he said.
"As a consequence the prison population is effectively managed and the use of accommodation is kept under regular review. Opportunities to improve safety at establishments is also reviewed. This includes the recently commissioned pilot of body worn camera to deter violent or disruptive prisoners".
She added: "Mechanisms for recording assaults, drug tests and use of Control and Restraint in prison has been improved in recent years and Northern Ireland Prison Service (NIPS) continues to analyse the factors involved and take action where required".
She said there was a "real and concerted effort to address the issue of substance misuse in prisons".