A Rochester hospital founded in the 19th century by nuns and W.W. Mayo will lose its name but not its Franciscan mission when St. Marys Hospital merges with Rochester Methodist, mostly in response to regulatory and reporting pressures.

The hospitals, which will take the name Mayo Clinic Hospital, are already staffed exclusively with Mayo Clinic doctors and operated by a single administrative team. But because of changes in health care regulation and a push for greater efficiency, they will now also become a single legal entity, the clinic said.

St. Marys, the home of the Mayo Clinic Psychiatry and Psychology Treatment Center and the Mayo Eugenio Litta Children’s Hospital, will keep its convent, chapel, daily Mass and crucifixes. The Sisters of St. Francis will remain.

“These sisters of faith, if you will, and the men of science kind of came together with a handshake and said ‘Well, we’ll do this,’ ” Dr. John Noseworthy, the president and CEO of Mayo Clinic, said of the hospital’s founding. “It’s a big part of our identity.”

The change will make it easier to report quality, financial and operating information, Noseworthy said. Because St. Marys and Methodist are separate legal entities, their financial information and statistics on certain procedures can be misleading.

For instance, most orthopedic surgery is done at Methodist, giving the false impression that St. Mary’s is not equipped for orthopedic surgery, even though the same doctors work at both hospitals.

Another reason for the transition is to make sure the Mayo Clinic operates efficiently, Noseworthy said.

“Everything we’re doing at Mayo Clinic is about unifying how we practice so we can provide better care at lower cost,” Noseworthy said. “Even having that separate license, it all gets in the way of our efficiency, so that’s the big driver.”

The Mayo brothers’ medical practice in Rochester preceded both hospitals, which were built in large part to accommodate Mayo patients. The Sisters of St. Francis opened St. Marys Hospital in 1889 on condition that Mayo provide the medical service. Rochester Methodist Hospital was opened in 1906.

In 1986, the Mayo Clinic, St. Marys and Methodist integrated their operations, but the two hospitals retained separate legal entities. That will change Jan. 1, 2014.

The change was approved by the Sisters of St. Francis, but not without some heartache.

“There’s a sadness in the sisters,” said Sister Marilyn Geiger. “But we’re very hopeful for the future.”

A memorandum of understanding between the Mayo Clinic and the Sisters allows the hospital to continue to not provide services prohibited by the Catholic Church, such as abortion, sterilization and stem cell procedures, Geiger said. Those services will still be provided at what is now Rochester Methodist.