Wearing white polo shirts with branding for Formula One watch sponsor Tag Heuer, jeans and sneakers, the men stood in front of the cars with placards to mark out the drivers' start positions.
A spokesman for the governing International Automobile Federation (FIA) said the decision had been taken by Michel Boeri, head of the organising Automobile Club de Monaco and of the FIA Senate.
Ferrari's Sebastian Vettel, a four-times world champion with Red Bull, jokingly offered his opinion.
"Why didn't we have any grid girls today? What was that?" asked the puzzled German. "You get there and park behind George or Dave. What's the point?"
Commercial supremo Bernie Ecclestone, who is usually prominent on the grid with accompanying celebrities but kept a low profile this time, was not immediately available for comment.
Mercedes motorsport head Toto Wolff, whose drivers Lewis Hamilton and Nico Rosberg were lined up on the front row of the grid, said the change had taken him by surprise as much as anyone.
"I have no particular view on this, but I was surprised to see them because we are used to good-looking girls without meaning in any way to be discriminatory," he said. "If it’s good-looking boys from time to time..."
The move comes after the FIA-sanctioned World Endurance Championship, which includes the Le Mans 24 Hours race on its calendar, this year decided to change its procedures and dispense with the familiar models.
WEC champion Anthony Davidson said at the time that the move was long overdue.
"It's old school to have such a concept as grid girls. Surely the world's moved on? And motor racing should follow quite closely what the rest of the world's doing in that respect," he told Reuters in April.
"I think that's a really nice touch, a modern touch as well, from the WEC to take that aspect of racing away. It is a bit sexist."
(Reporting by Alan Baldwin, editing by Pritha Sarkar)
