The 25-year-old was seen with Ronson at Le Baron nightclub in New York and fellow clubbers said they "couldn't get enough of each other", reported The Sun Online.
"Lindsay and Sam were whispering and laughing and they left the club holding hands. They didn't care who saw them and they definitely seem to be back on.
"It was just like the old days, they couldn't get enough of each other!" a source said.
The bisexual actress has been in the news for all the wrong reasons - she was charged with DUI and shoplifting recently and completed her probation in March.
The actress has landed the role of Elizabeth Taylor in the TV movie "Liz and Dick".