A committee will meet this week to launch a search for a successor to outgoing Yale-New Hospital President and Chief Executive Officer Joseph Zaccagnino. Zaccagnino announced last month that he will retire at the end of September, after more than 35 years with the hospital.

The committee includes members of the Yale-New Haven Hospital Board of Trustees and the Yale New Haven Health System board, and is led by hospital board chairman Marvin Lender and health system chairwoman Julia McNamara. The boards plan to select Zaccagnino’s replacement before Sept. 1.

Zaccagnino, who was named president in 1991 after serving as executive vice president and chief operating officer for 14 years, informed the hospital board of trustees of his decision to retire earlier this year. He said he plans to pursue other work in the future, including advisory positions and graduate-level teaching.

“My decision to retire was not an easy one, but it was made with the recognition that as time passes, the opportunities for new experiences and challenges as well as the flexibility to spend more time with family cannot be deferred indefinitely,” Zaccagnino said. “Although no longer leading two major health care organizations will provide a change in pace, I plan to continue to actively serve in the health care sector as an advisor to senior management and governing boards, by lecturing at the graduate level more frequently than has been possible recently and by serving on additional corporate boards.”

Zaccagnino has led the hospital through a period that has been marked both by extensive growth and protracted controversy. Under his leadership, the hospital has been ranked highly by publications like the U.S. News and World Report and developed plans for a $530 million cancer center. At the same time, it has faced a long struggle with employees and local activists over efforts to unionize its workers and its role in the community.

Zaccagnino said he will continue working with hospital leaders until September to advance Yale-New Haven’s current initiatives — including the effort to earn city approval for the cancer center — and create a smooth transition to new leadership.

Yale President Richard Levin said the committee will search for a strong leader to succeed Zaccagnino, who Levin said kept Yale-New Haven financially strong during a time when other hospitals have suffered setbacks.

“I will be serving on the search committee, which will hold its first meeting this week,” Levin said. “We will be seeking a leader who is eager to continue our progress toward becoming one of the nation’s leading centers for clinical medicine.”

Bill Meyerson, a spokesman for District 1199 Service Employees International Union, said the hospital’s rocky history with New Haven reflects badly on Zaccagnino. SEIU, which is leading the organizing drive at the hospital, and its allies have brought lawsuits and National Labor Relations Board charges against the hospital and protested in response to allegedly unfair employment and debt collection practices.

“The legacy of Zaccagnino is a mixed one, but on balance I would say that it is negative,” Meyerson said. “Under his stewardship and administration, the relationship between Yale-New Haven Hospital and the community, which includes its workers, was severely broken … His actions reflect a profound arrogance on the part of the city’s largest employer, and any hope we have for his successor is that they will find someone who is the opposite.”

Although Mayor John DeStefano Jr. has clashed with Yale-New Haven in recent months over its stance on unionization, the mayor said Zaccagnino has done his job well.

“I wish Mr. Zaccagnino well,” DeStefano said. “He’s worked hard to improve Yale-New Haven’s health care system and he’ll leave a lasting legacy. I look forward to working with his successor.”

Zaccagnino’s announcement comes as Yale-New Haven is still waiting for approval from the city’s Board of Aldermen to construct its proposed cancer center, a project hospital officials said they hope will break ground in September.

Yale-New Haven spokesman Vin Petrini said Zaccagnino’s retirement will not affect the cancer center plans.

“Both the board and [Zaccagnino] intend for the hospital to maintain a consistency of purpose and principle during this transition,” Petrini said.

The hospital has expanded under Zaccagnino’s leadership, opening new children’s and psychiatric hospitals and forming the Yale New Haven Health System in 1995.

During Zaccagnino’s time as president, the hospital has also bridged its clinical programs with those at the Yale School of Medicine, through a Yale New Haven Health System affiliation.

Medical School Dean Robert Alpern said he has forged a close relationship with Zaccagnino during the past year.

“Clinical practice at the medical school and hospital are really tied at the hip, and the quality of both programs are mutually dependant on each other, so it is important that the dean of the medical school and the hospital president have a close and a good relationship,” Alpern said. “We’re sad to see Joe step down … but we’re looking forward to the search. It will be important to find someone who is committed to maintaining this close relationship and working on creating an outstanding clinical program.”

Zaccagnino’s colleagues have said they will miss his presence at the hospital.

“Joe’s good humor, coupled with steadfast determination, has produced a legacy of strong, consistent performance at one of the nation’s premiere hospitals and health care systems,” McNamara said in a press statement.

During Zaccagnino’s tenure, New England’s first in vitro fertilization took place at Yale-New Haven, and the hospital became the first in Connecticut to perform bone marrow and heart-lung transplants.