The vice-chairman of the Assembly’s Health Committee has said he is horrified that patients' medical files were found in the rubble of Alasdair McDonnell MP's former GP surgery.
Sensitive medical records - including details of patients' miscarriages - were found on the demolition site on the Ormeau Road by children.
A journal with the hand written name "Dr McDonnell" and marked "confidential" contained the names and addresses of several women who appeared to have lost their unborn babies in the 1990s, the Irish News reported.
The paper said "several" bags filled with medical files were removed by a shredding company after a journalist arrived at the site.
SDLP leader Dr McDonnell, who used to part-own the surgery, has apologised.
He said: “This is a matter of the utmost seriousness and I am sincerely sorry for any anxiety or upset that may be caused to former patients.”
But Jim Wells, vice-chairman of the Assembly’s Health Committee, has described it as a "serious data breach" and said it must be fully investigated.
"Regardless of who the GP is or who manages the practice, the fact that very detailed medical information belonging to patients has been found on a building site is horrific," said the DUP South Down MLA.
"Some of the notes related to a patient who sadly had a miscarriage.
"I’m certain that the lady involved would be incredibly annoyed if such personal details fell into the wrong hands. People expect the health service to treat their data in a professional manner. Identity theft is rife throughout the world and a data breach like this would be a crime ring’s dream."
Mr Wells said it was alarming that electoral data was also found among the rubble.
"Why would a medical facility, paid for by the health service, have election materials in it?" he said.
"Was this facility used as some kind of election headquarters and if so was it declared in the electoral expenses? I sincerely hope that no other medical facility has files in it marked as a 'hit-list' with names, addresses and the individuals’ perceived voting intentions."
He said Dr McDonnell should refer himself to the Assembly’s Commissioner for Standards.
The health centre, on the lower Ormeau Road, has been derelict since 2005.
It was demolished in recent weeks after part of the building collapsed.
Dr McDonnell, who retired from the practice in 2009, said: "The medical practice, of which I was a part, had a responsibility to our patients to ensure that every piece of information was securely transferred to our new premises. I know that at the time those involved in the move believed that they had fulfilled this duty.
"It is evident now that somehow a small number of medical and personal files were not disposed of in the appropriate and secure fashion. This is a matter of the utmost seriousness and I am sincerely sorry for any anxiety or upset that may be caused to former patients.
"As soon as I was made aware I informed the Practice Head of the Medical Practice, from which I retired in 2009, who moved immediately to get a confidential shredding company on site to ensure that all papers are removed and disposed of without delay. I have also contacted Clanmill Housing Association to inform them that the site is not secure and that this presents a health and safety risk."
Clanmil bought the site from the Department of Health Social Services and Public Safety on April 11 this year to build 15 new flats.
A spokeswomen said: "Demolition of the building that formerly occupied the site commenced in June and our contractor has informed us that at no stage in the demolition were medical records found.
"In addition, the Department of Health has confirmed that it is confident that no medical or personal documents remained at 137-141 Ormeau Road prior to the sale to us.
"We understand that the adjoining doctor’s surgery at 143 Ormeau Road, which is adjacent to our site and which is not owned by us, is currently being demolished."