The film stars "Gossip Girl" actress Leighton Meester as a college freshman who becomes obsessed with her new roommate.
It debuted with $15.6 million.
The 3-D underwater cave adventure "Sanctum" debuted in second place with $9.2 million.
The romantic comedy "No Strings Attached" came in third with $8.4 million.
"The King's Speech" ranked fourth with $8.3 million, while "The Green Hornet" rounded out the top five with $6.1 million.
The top 10 movies of the weekend were:
1. "The Roommate," $15.6 million.
2. "Sanctum," $9.2 million.
3. "No Strings Attached," $8.4 million.
4. "The King's Speech," $8.3 million.
5. "The Green Hornet," $6.1 million.
6. "The Rite," $5.6 million.
7. "The Mechanic," $5.4 million.
8. "True Grit," $4.8 million.
9. "The Dilemma," $3.5 million.
10. "Black Swan," $3.4 million.
