Mike Tyson's fall was swift. Once the undisputed heavyweight champion of the world and the idol of every kid with a copy of Nintendo's "Punch-Out," he ended up bankrupt and addicted to drugs and sex. But now he's sober and coming off a stellar showing at the Sundance Film Festival, where "Tyson," a documentary about his life, was widely acclaimed.

These days, when young boxers ask him to go out on the town, his answer is uncompromising: "If I go out with you, I'm going to die."

"I can't afford to slip," Tyson explained to MTV News. "I probably don't have another line of cocaine in me. I don't got another shot of Hennessy in me. I don't have another case of sex addiction in me."

But with the success of the documentary comes renewed worries about the slippery slope of fame and addiction. "I was planning on moving back to New York City," he said. "I got here, and there was just too much going on here for me. I don't want to lose my girlfriend. I don't want to lose my relationship with my children. I could easily come down here, and as I walk down the street, people tell me how much they love me, how great I am. If I allow myself to really absorb that and find myself being some omnipotent individual and really saying, 'The hell with my girlfriend, the hell with my kids, I'll see them when I see them, and it's all about me.' I try to keep it as humble as possible."

During the interview, Iron Mike was candid about the connection for him between infidelity and drug use. "Some people say marijuana's a gateway to cocaine or heroin," he said. "No. To me, sex is my gateway.

"If I put myself around a situation where I have women and I'm attracted to someone," Tyson continued, "if I cheat on my girlfriend, I'll have so much pain that I will get high to kill that pain. And once I start getting high, it's a snowball effect and I won't come home because I'll be living in another world.

"That hour of pleasure's gonna be worth losing my world over?" he asked, shaking his head.

Despite the renewed attention from fans and media, Tyson has managed to stay clean. "I'm doing good now," he said. "I avoid all my pitfalls. ... I'm not pious or anything. I'm not weak. But I just try to keep it humble."