The 3,000-room resort was at near capacity Friday when the fire broke out midmorning, sending guests and employees onto the Las Vegas Strip where ashes and embers rained.
The blaze was contained within an hour.
An ambulance company spokeswoman said 17 people were taken to area hospitals with minor injuries, mostly from inhaling smoke or from fleeing the building. None of the 120 firefighters who fought the blaze was hurt.
The spectacle brought to mind the state's deadliest fire. In 1980, 87 people were killed in a fire at the old MGM Grand just down the street from the Monte Carlo.
Strict fire codes, including mandatory fire sprinklers, have since been adopted for the casinos on the Las Vegas Strip.
Fire Chief Steve Smith credited firefighters, not the sprinkler system for quickly containing Friday's fire.
He called it an exterior fire that consumed a foam-like building material. He said it was best fought from the interior. Firefighters entered top-floor rooms, broke windows and leaned out with hoses to aim water at the flames.
"It's very precarious up there," Smith said. "They did expose themselves to some extreme danger. They could have fallen out."
Smith said it was too early to assess damage or say what caused the fire, which began just before 11 a.m. There was no immediate indication of criminal activity or arson, but "nothing is ruled out at this time," he said.
Officials were told welders were working on the roof of the building before the fire, Clark County spokesman Erik Pappa said.
Ron Lynn, chief of the county Building Department, said five floors were affected by the fire, mostly from water damage, but only a few rooms had significant damage from fire and water.
Officials went door-to-door evacuating the hotel, said Gordon Absher, a spokesman for the resort's owner, MGM Mirage Inc.
Larry Wappel, 25, said he and his brother were in a room on the 30th floor when they heard housekeeping staff banging on doors and yelling "Fire, get out!" He said it took about 10 minutes to walk single-file down the stairs.
