An outstanding collegian at the University of Kentucky, Issel was twice named an All-American en route to a school-record 25.7 points per game for his career.

Upon Issel's retirement from the NBA in 1985, Wilt Chamberlain, Kareem Abdul-Jabbar, and Julius Erving were the only professional basketball players to have scored more career points.

[2] Issel attended Batavia High School, graduating in 1966 as an All-American playing for coach Don Vandersnick.

[7] Issel was at the UK from 1966 to 1970 and scored 2,138 points (an average of 25.7 per game) and had 1,078 rebounds, while being named an All American for two of the three seasons he was eligible for the award.

[8] According to Sports Illustrated Magazine, in a game early in Issel's Kentucky career, teammates were neglecting to give him the ball.

"[9] On February 7, 1970, Issel scored 53 points in a 120–85 victory over Ole Miss, breaking Cliff Hagan's single-game record of 51.

[11] Issel's career at Kentucky coincided with that of Pete Maravich at SEC rival LSU, who scored an NCAA-record 3,667 points (44.2 per game).

A three-year starter for Kentucky, Issel led his team to three Southeastern Conference titles and set 23 school records in his career.

[12] Helped by dominant 7'2" center Artis Gilmore, the 1974–75 Kentucky Colonels won the 1975 ABA championship, with key support from Issel and sharp-shooting guard (and fellow ex-Kentucky Wildcat) Louie Dampier.

Prior to the 1975–76 season, the Colonels traded Issel to the Baltimore Claws (formerly the Memphis Sounds) for Tom Owens and cash.

The Claws folded before the season's start, and Issel was subsequently traded to the Denver Nuggets for Dave Robisch and cash.

Issel played a key role in helping the Nuggets make the postseason every year of his tenure,[13] alongside (at various points) fellow stars David Thompson, Bobby Jones, Kiki Vandeweghe, and Alex English.

On January 31, 1980, Issel scored an NBA career high 47 points, including making 19 of 23 free throw attempts, in a 127–126 win over the New Jersey Nets.

[18] On January 21, 1981, Issel grabbed an NBA career high 21 rebounds, while also scoring 32 points, during a 129–115 win over the San Antonio Spurs.

He accumulated over 27,000 points in his combined ABA and NBA career, trailing only Kareem Abdul-Jabbar, Wilt Chamberlain and Julius Erving upon his retirement.

He resigned 34 games into the 1994–95 season after facing criticism for his coaching style, saying the pressures of the job "have started to make me something I don’t want to be.”[23] Issel returned to the Nuggets in 1998 as president and general manager.

Just before the start of the 1999–2000 season, he told reporters that there were several decisions he simply couldn't make due to the unstable ownership situation.

On December 11, after a close loss to the Charlotte Hornets, Issel heard a fan taunting him, as he walked off the court at the Pepsi Center.

[5][6] In February 2018, Issel became president of the Louisville Basketball Investment and Support Group, a Kentucky-based company founded in 2016 to pursue an NBA franchise.