Cláudio Kestener started swimming at the Pinheiros school and, at the age of seven, he started to compete; at age 16 he participated in his first international competitions. In 1980, at the Latin Cup in Spain, he broke the Brazilian record for the 100-meter butterfly.[3]
In 1981 he was the Brazilian record holder of the 100-metre butterfly, with a time of 57.12 seconds.[6]
He started engineering school the same year he returned from the Moscow Olympics and decided to dedicate himself to his studies. During college, he participated in the University Games and gradually moved away from competitive swimming.[3]