The Quakers won 71 Ivy League championships during his tenure, including nine in men's basketball and eight in football.
"Being an athletic director today is a very complex job, much more than when I started," Bilsky said Thursday. "But it's easier when you're working for your school than if you're just in a job. . . .
"It's a tough job. But it kept me motivated doing it for my school. That's why I came back to Penn and why I stayed for as long as I did."
Bilsky said he had been considering retirement for close to a year, and decided to announce it at the conclusion of the recent fund-raising campaign.
"You always look for ways to measure success," he said. "We've had 21 different sports win championships. At the same time, we've won the most football and basketball championships of anyone. The combination of being really good in the most visible sports but not at the expense of broad-based success makes me feel very good about what we achieved."
Bilsky said he thought that his administration made progress in the area of gender equity, that "regardless of gender, the athletes felt like we cared about them, and it's one of the real positives for us."
Bilsky also helped the Ivy League on a larger scale. He served on a committee that completed a national television deal with NBC Sports Network. He also was instrumental in persuading the league to establish a digital broadcast platform that was launched this year.
"He's very business-savvy and definitely has been instrumental in the development of our television package with NBC Sports," Ivy League executive director Robin Harris said.
Al Bagnoli, who served as Penn's football coach for the entire length of Bilsky's tenure, called him "a tremendous supporter of our football program and our entire athletic department. His guidance, vision, leadership, and commitment to our student-athletes and coaches has been extraordinary."
Jerome Allen, whom Bilsky watched play basketball for Penn and later hired as head coach, said he owed him "a huge debt of gratitude" for naming him as coach in a sport "that both of us - along with so many others - hold dear to our hearts."
In a statement, Penn president Amy Gutmann said Bilsky "has lived and loved Penn athletics, and the university has been incomparably the better for it."