The current Miss USA, Tara Conner, is to keep her title despite allegations of underage drinking, drug abuse and speculation about her love life.
She won a second chance after a crisis meeting with Donald Trump, who owns the Miss Universe beauty pageant contest.
Kentucky-born Miss Conner has become a regular on the New York party scene and a fixture in US tabloid newspapers since winning her title in April.
She only turned 21 ,the legal drinking age in New York state, on Monday.
Mr Trump summoned Miss Conner to a Manhattan meeting on Tuesday, amid speculation that the beauty queen would be stripped of her title.
Instead Mr Trump declared: "I've always been a believer in second chances."
He said Miss Conner had become caught up in the "whirlwind" of a New York lifestyle, and added that she would not get another chance.
A tearful Miss Conner, her voice breaking with emotion, thanked Mr Trump, saying: "I swear I will not let you down."
Last week Mr Trump was reported to be "seriously studying the situation", after becoming concerned at Miss Conner's personal conduct.
Winners of the Miss USA title, part of the wider Miss Universe competition, are expected to abide by a code of moral behaviour.
Under the terms of their year-long contracts, the winners are required to take part in a host of public engagements for the beauty pageant organisers.
Miss Conner, by contrast, has ended up in American tabloids for all the wrong reasons.
She has developed a reputation as a party girl after being spotted dancing and drinking in a string of New York nightclubs and bars.
There have been allegations of drug abuse and reports of scandalous behaviour in Trump Tower, where pageant winners receive a grace-and-favour apartment for a year.
Miss Conner and another winner, Miss Teen USA, were told to leave their shared apartments after they were reportedly spotted kissing in public.
Last week Miss Conner retreated from Manhattan as calls grew for her to relinquish the title, heading back home to Kentucky.