Credit: Mavrix Online

Marissa Cooper returns!

Mischa Barton was all smiles lounging in a beach chair in Miami, Fla. on Tuesday.

And why not? The sometimes-troubled star, 25, looked the slimmest she has since her days as the buzzed-about star of The OC. Clad in a skimpy two-piece bikini, Barton grinned from ear-to-ear behind her sunglasses, showing off taut abs and more.

Barton, whose weight has fluctuated since her heyday, recently wrapped filming her role as the beautiful love interest in the flick The Misadventures of Ben Blanks.

She checked into a psychiatric hospital in 2009, and opened up about her battle with depression in fall 2010.

Tell Us: How do you think Barton looks these days?