With that surprising diagnosis for one of nascar's brightest young stars. 22-year-old trevor baynes was the youngest driver to win the daytona 500. And has now revealed he has multiple sclerosis.... See More
With that surprising diagnosis for one of nascar's brightest young stars. 22-year-old trevor baynes was the youngest driver to win the daytona 500. And has now revealed he has multiple sclerosis. Abc's john muller has the story. Reporter: His need for speed has propelled him to fame. At 20 years old, trevor bayne, became the youngest ever to win the daytona 500. But he's hit a bump in the road. Announcing he has been diagnosed with multiple sclerosis. In 2011, going to the mayo clin clinic, after being out of the race car with double-vision. Reporter: Bayne's little sister also has m.S., And was diagnosed this summer, after the double-vision and fatigue started affecting his driving. But the 22-year-old says his illness won't slow him down. I hope not. Our job is to go very fast. M.S. Can have a variable course. One person can have years where they're not affected much at all. Where someone else, the same age, presenting at the same time, can have a course that's rotten. Reporter: With the green light from doctors and nascar to keep racing, he'll compete in the sprint cup series and beyond. I've been racing since I was 5 years old. And this doesn't change a thing. I want to do what I've dreamed of. We have high hopes that we can continue to do that. Reporter: It's the same competitive experience that robin got to experience firsthand, when she challenged him to a go-kart race in 2011. I got two. Reporter: And while the challenge is more daunting, bayne says he is determined to switch gears and use his diagnosis as a way to help others. We get to focus on the race wins and everything else. It's something I want to be able to share with people. I know people can relate to struggles. Reporter: Confident it will be nothing more than a mere pit stop in life. For "good morning america," john muller, abc news, new york.
This transcript has been automatically generated and may not be 100% accurate.