The star was released from house arrest on Wednesday after being confined for 35 days for pleading 'no contest' to misdemeanour necklace theft, and headed straight out to celebrate.
Lohan, 24, was spotted at the hotspot Lexington Social House, where friend Lyndsy Fonseca was holding a party that she had postponed so that Lohan could attend.
An onlooker told People that the actress, who is no longer banned from drinking, was enjoying a cocktail and mingling with her mates.
'She was in a good mood. She definitely seemed happy to be free and out celebrating with friends,' said the witness.
Lohan later Tweeted details of her outing, 'Of course me going to my best friends going away dinner is a headline. Nothing exciting happened aside from the very yummy hummus and pita.'
She will remain on probation for the next three years thanks to two DUI cases in 2007 and will have a progress review on July 21. She is no longer subject to random drug and alcohol tests.