The critical consensus on Rotten Tomatoes states that "Will Ferrell and John C. Reilly have undeniable comic chemistry, but Step Brothers squanders their talents on lowbrow humor that's more juvenile than funny." The film holds a score of 55% based on 215 reviews, with an average rating of 5.70/10. Metacritic gives the film a score of 51 out of 100 based on 38 reviews, indicating "mixed or average reviews."
Roger Ebert of the Chicago Sun-Times gave the film a score of 2.5 out of 4, saying that "the movie is only fitfully and sporadically funny, which is surprising considering the cast and talent involved." Peter Travers of Rolling Stone gave the film a score of 2.5 out of 4, saying that "the laughs come fast and furious, but they're rarely inspired." Justin Chang of Variety called the film "a raunchy, lowbrow comedy that's often painfully unfunny but also frequently hilarious."
Despite the mixed critical reviews, "Step Brothers" was a commercial success, grossing over $128 million against a production budget of $65 million. The film has since gained a cult following and is considered by some to be a modern comedy classic.