BISHOP of Derry Seamus Hegarty has written to Pope Benedict with his resignation on health grounds, the Catholic Church has confirmed.
The senior cleric said he was no longer fit to fulfil his diocesan duties after being diagnosed with an irreversible illness.
"Very recently, I received a diagnosis of a condition which is, unfortunately, irreversible and progressive. I am now receiving treatment for this condition," he said.
Bishop Hegarty, who was in charge of the Raphoe Diocese in Donegal from March 1982 before moving to Derry to take up his post in November 1994, is 71.
"I had hoped to continue until the age of 75 as diocesan bishop, but my medical condition is such that I have an obligation to submit my resignation," he said.
"Due to my condition, I will have to scale back on my duties while the Holy Father considers my letter of resignation. It is my hope that my resignation will be accepted. It is my intention to maintain a pastoral ministry, to the extent that I am able, into the future. I ask for prayers at this time."
Bishop Hegarty began undergoing medical tests earlier this year but has only now confirmed he has been diagnosed.
He said he was following the Code of Canon Law in which a bishop is "earnestly requested to offer his resignation" when, because of illness, he becomes unsuited for the fulfilment of his office.
The Pope will make the final decision on whether Bishop Hegarty should continue to head the diocese.
Bishop Hegarty was born in 1940 and ordained a priest on June 19 1966.