The movie has received 170 consecutive positive reviews from critics as of Tuesday morning, earning no "rotten" ratings and surpassing Toy Story 2 as the best-reviewed movie on the site.
Instead, it's a coming-of-age tale about a teenage girl who has a tense relationship with her mother.
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Lady Bird has become the best-reviewed movie of all time of Rotten Tomatoes
"It's awesome", Gerwig told Vanity Fair, adding that her younger brother had told her the news and even he was "slightly skeptical" that her film had beat the animated movie.
The movie, which was released in the U.S. earlier this month, has achieved a 100 percent score from the aggregation site, and is the most reviewed film to have done so. The New York Times described Ronan as 'one of the most formidable actors in movies today' in their review of the title.
"Lady Bird", Greta Gerwig's coming-of-age film about a teen with a penchant for Dave Matthews Band, puffing on fiberglass and throwing herself out of the occasional moving vehicle has broken a Rotten Tomatoes record.
Released by indie film studios A24 (Moonlight) earlier this month, Lady Bird only went from a limited release to wider distribution this past weekend, and the film has so far pulled in $10.7 million in domestic theaters, according to Box Office Mojo.