Winthrop-University Hospital — a major health-care force on Long Island for 120 years — signed an affiliation agreement Wednesday with NYU Langone Medical Center in Manhattan, creating the second-largest health system in Nassau and Suffolk counties.

“We are very excited. It’s really a beautiful merger of philosophies,” said John Collins, Winthrop’s president and chief executive. “Both sides are excited. We feel that we are doing the right thing for the community and we intend to be here for the next 100 years.”

Northwell Health, which combined the North Shore and Long Island Jewish medical systems, is the largest on the Island.

Talks between Winthrop and NYU Langone began in July, when Winthrop executives announced signing a “non-binding” letter of intent.

Winthrop will become NYU-Winthrop as a result of the affiliation, which immediately integrates the two organizations’ physician networks in Nassau and Suffolk counties, New York City and elsewhere in the region, officials for both institutions said.

The Mineola-based medical center currently generates $1.3 billion in revenues, while NYU Langone produces $7.5 billion. A full merger will occur over five years, Collins said.

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Dr. Robert I. Grossman, dean and chief executive of NYU Langone, said that in negotiating the agreement, “We quickly realized that an affiliation would allow our institutions to enhance the range and quality of services offered to the residents of Long Island, as well as grow key ambulatory services and the physician network across the region, with Winthrop as the primary inpatient hospital.”

The organizations are giving themselves a five-year horizon because merging two institutions “doesn’t happen overnight,” he said.

“There is a lot of time and planning that goes into the cultural alignment and making sure that everything is connected together,” Grossman said. “We want to make sure that all the i’s are dotted and t’s are crossed and that we have a common culture and shared values.”

Collins said he will continue as Winthrop’s president and chief executive, reporting directly to Grossman.

The Long Island hospital remains under the direction of its current board of directors and administrators. One member from Winthrop’s board will take a seat on NYU Langone’s board, and several members of NYU Langone’s board of directors will be seated on the Long Island hospital’s board. The number of NYU Langone board members who will have seats at Winthrop was not released Wednesday.

NYU Langone already has 150 ambulatory sites throughout the region and 40 affiliated physician practices on Long Island and in Queens. Winthrop has 61 ambulatory sites and 250 affiliated physician practices, with offices reaching from Shelter Island into Manhattan, Collins said.

Winthrop was founded in 1896 as the Island’s first community hospital by a group of physicians and has grown into a 591-bed teaching hospital and home to a major, 7,500-square-foot trauma center.

The main campus includes a dialysis center and a CyberKnife facility where precision radiation treatment is performed for certain cancers. The hospital also is home to the Cancer Center for Kids.

Elsewhere in Nassau and Suffolk, Winthrop operates ambulatory facilities, such as a newly expanded surgical center in Garden City and its Specialty Center in Deer Park.

Currently, Winthrop’s key affiliation as a teaching institution is with Stony Brook University School of Medicine. With the NYU partnership, the hospital’s faculty will retain appointments within Stony Brook. About 80 third- and fourth-year Stony Brook medical students are trained on the Winthrop campus.

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Grossman noted that as part of the new agreement, NYU medical students also will have the opportunity to train under Winthrop physicians.

It is not yet known if Winthrop will retain the words “University Hospital,” or if it will be defined as a medical center or as something else, such as the NYU Winthrop Health System.

Signage is not expected to change until the affiliation is finalized — probably sometime in the spring, pending completion of state and federal regulatory requirements, officials said.