Ridden by jockey Don Brumfield, Kauai King won the 1966 Kentucky Derby and Preakness Stakes but finished 4th in the Belmont Stakes at Aqueduct Racetrack, 2 lengths back of the winner, Amberoid. On June 16th, the colt was sold to a horse breeding syndicate for a then record price of $2,520,000.
1966 was also the 3-Year-Old season for the outstanding colt, Graustark, as well as the 1965 Champion 2-Year-Old Colt, Buckpasser. The undefeated Graustark's racing career ended with a broken coffin bone in the Blue Grass Stakes and an injury kept Buckpasser out of the Triple Crown races. After Kauai King's wins there was much speculation as to which was the better horse and on June 27, 1966 Kauai King and Buckpasser met in the Arlington Classic. Kauai King's racing career came to an end when he pulled a ligament in his leg during the race. Following the announcement of his career-ending injury, he was retired to stand at stud at Alfred G. Vanderbilt II's Sagamore Farm in Glyndon, Maryland.
Kauai King proved less than successful as a sire. Near the end of 1971 it was announced the horse was being shipped to stand at stud in England. He remained there until 1973 when he was sent to a breeding farm in Japan where he died on January 24, 1989.