Writing for "The A.V. Club", Emily VanDerWerff rated the episode an A, calling it "an occasionally beautiful, occasionally haunting, often overwritten story". She felt that the episode took the uncommon route of tying together several previously-mentioned aspects of the series' mythology, making it "easy to believe the pieces might come together at this point". However, VanDerWerff also noted that the episode's two main plot threads—Scully's cancer and Mulder's investigation—seemed "clumsily grafted" together, and did not explore the theme of living with the fear of death as well as the previous episode, "Never Again", had done. Frank Spotnitz praised the episode, saying, "I think that was the best mythology episode we ever did. It's my favorite one". Chris Carter has stated that he feels "Memento Mori" ranks "among the best mythology episodes of all nine seasons".