oh. What a relief it is. Next tonight, one of the most admired actors in the world, tom hanks decided to talk about something private, his health. What he said could happen millions of other americans... See More
oh. What a relief it is. Next tonight, one of the most admired actors in the world, tom hanks decided to talk about something private, his health. What he said could happen millions of other americans with type two diabetes who want to gain control of their lives. Abc news gio benitez with the story. Reporter: As tom hanks battled pirates in his new high seas drama, behind the scenes the star was confronting a personal battle, a secret he revealed on the late show with david letterman. I went to the doctor and he said you know those high blood sugar numbers you've been dealing with since you were 36? Well, you graduated. You've got type two diabetes, young man. Reporter: The 57-year-old actor, now one of the nearly 18 million americans facing a new reality, type two diabetes. It's the most common form of the disease. Blood sugar levels surge. He joked about his condition with letterman. My doctor said, look, if you can weigh as much as you weighed in high school, you will essentially be completely healthy and will not have type two diabetes and I said I'm going to have type two diabetes. Reporter: We've seen him gain 30 pounds for a league of their own, dropped 30 the next year for philadelphia and for cast away he began shooting 40 pounds overweight before losing 50 to play a man left stranded for years, an extreme hollywood version of the yo-yo dieting many americans experience. That in itself doesn't cause diabetes, as long as you don't let those extra pounds stay with you for long. What you are saying is the clock is ticking? The clocking ticking if you have got excess body weight. If that weight sits, chances are the body is going to adopt that higher body weight. You're talking, what, a year? Probably about a year depending on the individual. Reporter: Tonight hanks tweeting, yep I have type two diabetes. Type one is very serious. Type two I can manage with very good habits. High shall.
This transcript has been automatically generated and may not be 100% accurate.