A prisoner was on the roof of Mountjoy jail for just over four hours after attempting to retrieve a suspected drugs parcel.
The inmate climbed up on top of the D division of the Dublin complex before lunch and was taken back inside at about 4pm.
A spokesman for the Irish Prison Service said a decision was taken by the jail management not to reopen prisoners' cells after lunch as they dealt with the incident.
It is understood prison staff were concerned the inmate may have been under the influence of drugs after retrieving a package of contraband that had been thrown over the prison walls.