Harold and Maude received mixed reviews, with several critics being offended by the film's dark humor. Roger Ebert, in a review dated January 1, 1972, gave the film one-and-a-half out of four stars. He wrote, "And so what we get, finally, is a movie of attitudes. Harold is death, Maude life, and they manage to make the two seem so similar that life's hardly worth the extra bother. The visual style makes everyone look fresh from the Wax Museum, and all the movie lacks is a lot of day-old gardenias and lilies and roses in the lobby, filling the place with a cloying sweet smell. Nothing more to report today. Harold doesn't even make pallbearer." Vincent Canby also panned the film, stating that the actors "are so aggressive, so creepy and off-putting, that Harold and Maude are obviously made for each other, a point the movie itself refuses to recognize with a twist ending that betrays, I think, its life-affirming pretensions."
The reputation of the film has increased greatly; Rotten Tomatoes, which labeled the film as "Certified Fresh", gave it a score of 84% based on 45 reviews, with an average score of 7.7/10. A consensus on the site read, "Hal Ashby's comedy is too dark and twisted for some, and occasionally oversteps its bounds, but there's no denying the film's warm humor and big heart." In 2005, the Writers Guild of America ranked the screenplay #86 on its list of 101 Greatest Screenplays ever written. Sight & Sound magazine conducts a poll every ten years of the world's finest film directors, to find out the Ten Greatest Films of All Time. This poll has been going since 1992 and has become the most recognized poll of its kind in the world. In 2012, Niki Caro, Wanuri Kahiu, and Cyrus Frisch voted for "Harold and Maude". Frisch commented: "An encouragement to think beyond the obvious!" In 2017, Chicago Tribune critic Mark Caro wrote a belated appreciation, "I'm sorry, Harold and Maude, for denying you for so long. You're my favorite movie once again."