The 29-year-old "O.C." star sizzled in a crimson 2-piece on the powdery Caribbean sands. And she's been spotted in a range of different suits over the course of her beach getaway -- notably in a black string bikini and a scarlet halter style.
This is the second stop on Bilson and Christensen's island-hopping adventure. The on-again-off-again couple made a first stop on the island of Manhattan, jetting from their home town of Los Angeles to the Big Apple on Thursday for Bilson's Magnum ice cream campaign premiere with uber-designer and director Karl Lagerfeld at the Tribeca Film Festival.
Incidentally, Bilson reported eating 25 ice cream bars over the 3 days of filming. We see the binge didn't affect her rockin' bikini body!
From New York, the duo headed to their tropical-isle getaway for an early birthday celebration (Christensen doesn't turn 30 until Tuesday.) They've been spotted hanging on the golden-sand beach, playing in the waves and looking relaxed and happy while hiking around taking in the sights and shopping.
Don't miss our gallery of stars in bikinis, below!
Stars in Bikinis
See Rachel Bilson and other stars as they bare it all in bikinis.
And hear what the actress has to say about working with Lagerfeld and her newest TV pilot, "Hart of Dixie."