A late-night visit to Children’s Hospital Boston more than 30 years ago with his infant son led Stephen Karp to a long history serving on two of the hospital’s boards.

Karp, chairman and CEO of New England Development, joined the Children’s Hospital Board of Trustees in 1990 and has been chairman since 2004. He took a break from the hospital board between 1998 and 2004 to serve as the chairman of the Children’s Hospital Trust, which he founded.

Karp was honored this year by the New England chapter of the National Association of Corporate Directors for his involvement with such organizations as Union College, Boston University, Belmont Hill School, Boston Symphony Orchestra and Newton-Wellesley Hospital.

But it’s his work with Children’s Hospital that he says defines him.

“I have a passion for children but Children’s Hospital, in particular,” said Karp. “I have a feeling of accomplishment and pride and investment all the time.”

Karp and his wife, Jill, were living down the street from Children’s when their baby took ill late at night. The worried new parents rushed the child to the hospital.

The illness wasn’t serious, and as the Karps were leaving the hospital the following morning, they ran into an acquaintance. The woman was involved with the Children’s Hospital League and invited Jill Karp to the next meeting. Jill Karp eventually became president of the League.

“I got invested after that and have been ever since,” Stephen Karp said.

In November 2002, the Karp Family Foundation donated $15 million for the Karp Family Research Laboratories, a 12-story facility that added 680,000 square feet of research space to the hospital. From 2000 until 2005, Karp spearheaded the Cause for Wonder Campaign, which raised $311 million for buildings, programs and an endowment.

In 1998, Karp launched the Children’s Hospital Trust, and as board chairman, he helped the hospital’s fundraising soar to $95 million in 2008 from $13 million in 1997.

“I guess the tag line I would use for him is that he leads with his heart,” said Jim Mandell, CEO of Children’s. “I don’t think we’d be where we are today if it wasn’t for him.”

Over the 20 years Karp has been involved with Children’s, he has seen its research capacity increase and its care in inner city neighborhoods expand. In addition, Karp has helped guide the hospital’s growth onto new campuses in Waltham and Peabody.

“Every time I go to the hospital, it gives me a feeling that I’m a little bit a part of helping the kids,” said Karp. “You know why you’re there. It’s worth the time and effort.”