The Liz & Dick actress reportedly got together with her popstar friends at the Chateau Marmont hotel in Los Angeles to enjoy an evening of games and films.
"[They were] watching old movies and playing board games [at the] slumber party," a source told X17 Online.
"The three of them had dinner in the garden on Tuesday night at Chateau, and then Lindsay and GaGa ran upstairs to play dress up and came down in different outfits."
Lohan later sent a Twitter message to GaGa which seemed to reference an inside joke, writing: "#skinnysnack1 @ladygaga hahaha."
Earlier this week, GaGa launched her own social network for her Little Monsters.
Lohan was recently rumoured to be in talks to star in Scary Movie 5.
Watch the video for Lady GaGa's 'Eh, Eh (Nothing Else I Can Say)' below: