The event, called "Monstrous Summer All-Nighter," was a nod to Disney's upcoming movie, "Monsters University," KTLA-TV, Los Angeles reported Friday.
Large crowds camped out outside the theme park Thursday night to be among the first inside when doors opened at 6 a.m. Friday, KTLA said.
Disneyland had the same 24-hour opening kickoff last year, and so many people turned up, some were turned away when the park reached capacity.
Disneyland spokeswoman Suzi Brown said more police officers were brought in this year, and staff were required to park off-site to accommodate for the influx of customers.
"We worked really well with the city of Anaheim this year and traffic control to help mitigate all those problems," she said.
Disney World in Orlando, Fla., was also open for 24-hours straight to kick off its summer season as well, KTLA said.