Montefiore Medical Center in the Bronx is expected to open a fourth division of its 1,100-bed hospital today, as it takes over the nearby Our Lady of Mercy Medical Center just after the stroke of midnight.

With the $38 million transaction complete, Montefiore will unveil a new sign for what will be known as the hospital’s North Division. Our Lady of Mercy, a 369-bed facility, is situated about a mile north of Montefiore’s main campus in the Norwood section of the Bronx.

The deal includes 2,500 Our Lady of Mercy employees and more than 500 physicians, who will work at Montefiore. Following the acquisition, Montefiore will have 1,491 beds and 46 operating rooms, in addition to more than 16,000 employees and more than 2,600 physicians on its staff.

Details about what role the North Division will play in Montefiore’s overall health care system are not yet clear, but Montefiore’s president, Dr. Steven Safyer, said it is likely to become a “place where we do more community-based hospitalizations and care.”

The deal, which has been in the works for several years, accelerated when Our Lady of Mercy filed for bankruptcy protection in 2007. “It wasn’t financially viable,” Dr. Safyer said.

Dr. Safyer said his first priority is to ensure uninterrupted care for Our Lady’s patients. “It is first and foremost a needed community service,” he said.

But the transaction also enables Montefiore further to regionalize the care it presently provides at its network of health clinics and at three current campuses, including the Children’s Hospital at Montefiore, the Moses Division Hospital, and the Weiler Division Hospital.

Dr. Safyer said Montefiore would invest about $100 million over the next five years to improve the hospital’s aging facilities. Montefiore has already upgraded Our Lady of Mercy’s clinical information system.