During his first year of varsity basketball at the University of North Carolina at Chapel Hill in 1955, Rosenbluth was the Tar Heels' leading scorer. In his senior year he averaged 28.0 points per game and led UNC to a perfect 32-0 record and its first NCAA Championship. He set the ACC record with 2,045 career points. Rosenbluth holds UNC records for most points in a single season (897) and highest single-season scoring average (28.0 PPG)

Lennie was the recipient of the Helms Player of the Year Award in 1957 and named ACC Player of the Year that same year. He was also MVP '57 ACC Tournament.

Until 1992, Rosenbluth was the only collegian to be named NCAA National Player of the Year, ACC Player of the Year, ACC Tournament MVP, and NCAA regional MVP in the same season. His feat has since been matched by Christian Laettner of Duke University and UNC's Antawn Jamison. His No. 10 jersey was retired by UNC.

Died June 18, 2022, at the age of 89