Reigning queen Nana Meriwether will relinquish her crown and the posh New York apartment that comes with it and usher in her successor during the competition Sunday evening at the Planet Hollywood hotel-casino on the Las Vegas Strip.
Most of the competitors will be quickly sent home.
Contestants will be whittled to 15 after the event's opening fashion show with judging decisions based on competitions and interviews done during the week before the telecast. The remaining contestants will vie for the crown in three arenas: swimsuit, evening gown and interview question.
Contestants cannot have been married or have children, and they must be younger than 27.
Unlike the rival Miss America pageant, Miss USA does not ask its queens to perform a talent or choose a charity mission.
The judge's panel includes over-the-top fashion designer Betsey Johnson, "Biggest Loser" star Bob Harper and "Wait Wait ... Don't Tell Me" personality Mo Rocca.
The pageant airs live on NBC, hosted by Nick Jonas of the Jonas Brothers pop act and Giuliana Rancic, co-anchor of "E! News" and featuring performances by the Jonas Brothers and DJ Pauly D. The network co-owns the parent Miss Universe Organization with Donald Trump.
The winner will represent the United States at the Miss Universe pageant in the winter.
Last year's Miss USA, Olivia Culpo, won that international crown, becoming the first Miss USA to ascend to Miss Universe in 16 years.
The night's winner also becomes a spokeswoman for breast and ovarian cancer awareness and other causes, while traveling to promote the organization.
The Miss USA hopefuls have been staying at the Planet Hollywood casino for the past week, but the flashing slot machines and ubiquitous oversized novelty drinks have been little more than a background to a stuffed schedule of product tie-in media events, including hairdo contests and paddleboat competitions.
The animal rights organization People For The Ethical Treatment Of Animals is using the pageant to stage a protest of fur and the tradition of awarding furs to winners of some state pageants.
PETA has made a provocative ad featuring four nude former Miss USA winners. The tagline is: "Feel Beautiful in Your Own Skin, and Let Animals Keep Theirs."