The inquiry was carried out by the Apostolic Visitation to Ireland and involved teams visiting all four Catholic archdioceses, seminaries and religious congregations.
The Irish bishops will give their reaction to the findings at a press conference in Maynooth this morning.
Michael Kelly, deputy editor of the Irish Catholic, said he expects the report will call for a dramatic change in the structure of the Church.
"One of the proposals, I would expect, would be that the number of dioceses - currently standing at 26 - will be cut dramatically, possibly to as few as 12," Mr Kelly said.
"That obviously would mean dramatic cuts in the number of bishops.
"I don't expect that will mean any bishops being fired," he added. "We currently have seven Irish dioceses awaiting the appointment of a new bishop.
"I think they'll probably achieve this reform by natural wastage."