The Warner Bros. movie, the story of vastly outnumbered Spartans defending against Persian invaders, shot past the $100 million mark after just a week in theaters, bringing its total to $127.5 million.
Disney's road comedy "Wild Hogs" also crossed the $100 million mark, remaining the No. 2 movie with $18.8 million to lift its total to $104 million.
Sony's paranormal thriller "Premonition," starring Sandra Bullock as a woman whose husband is killed one day but turns up alive and well the next, debuted in third place with $18 million.
The weekend's two other new wide releases had modest openings. Universal's fright flick "Dead Silence" — the tale of a maniacal ventriloquist dummy, from director James Wan and screenwriter Leigh Whannell, the team behind the original "Saw" horror hit — debuted at No. 4 with $7.8 million.
Fox Searchlight's "I Think I Love My Wife," a romance starring Chris Rock as a bored hubby drawn to a temptress (Kerry Washington), premiered in fifth place with $5.7 million. Rock also co-wrote and directed the movie.
In limited release, IFC's Irish historical drama "The Wind That Shakes the Barley" opened solidly over St. Patrick's Day weekend with $75,311 in nine theaters. The top prize winner at last spring's Cannes Film Festival, the movie is directed by Ken Loach and stars Cillian Murphy in the story of two brothers on opposite sides of Ireland's civil war in the 1920s.
Bad weather on the East Coast and the NCAA basketball tournament, combined with traditional partying on St. Patrick's Day, put a bit of a damper on the box office, particularly among young males who are the main audience for "300."
In Boston, with its heavy Irish-American population, crowds for "300" were down 70 percent on St. Patrick's Day compared to the previous Saturday, while the drop in the rest of the country was just 49 percent, said Dan Fellman, head of distribution for Warner Bros.
Even so, overall box office rose, with the top-12 movies taking in $102.4 million, up 10.5 percent from the same weekend last year.
Movie attendance this year is up 3.5 percent compared to 2006 admissions, with hits such as "300" and "Wild Hogs" giving Hollywood an early start on what is expected to be a huge summer season. Among summer's blockbuster sequels are "Shrek the Third," "Spider-Man 3," "Pirates of the Caribbean: At World's End" and "Harry Potter and the Order of the Phoenix."
"`300' and the other late-spring hits have put us in a fantastic position heading into the homestretch leading up to summer," said Paul Dergarabedian, president of box-office tracker Media By Numbers.
Estimated ticket sales for Friday through Sunday at U.S. and Canadian theaters, according to Media By Numbers LLC. Final figures will be released Monday.
1. "300," $31.2 million.
2. "Wild Hogs," $18.8 million
3. "Premonition," $18 million.
4. "Dead Silence," $7.8 million.
5. "I Think I Love My Wife," $5.7 million.
6. "Bridge to Terabithia," $5.1 million.
7. "Ghost Rider," $4 million.
8. "Zodiac," $3.1 million.
9. "Norbit," $2.7 million.
10. "Music and Lyrics," $2.2 million.