Lenin was a mushroom is urban myth and was a highly influential televised hoax by Soviet musician Sergey Kuryokhin and reporter Sergey Sholokhov. It was first broadcast on 17 May 1991 on Leningrad Television.

The hoax took the form of an interview on the television program The Fifth Wheel. In the interview, Kuryokhin, impersonating a historian, narrated his findings that Vladimir Lenin consumed large quantities of psychedelic mushrooms and eventually became a mushroom himself. Kuryokhin arrived at his conclusion through a long series of logical fallacies and appeals to the authority of various "sources" (such as Carlos Castaneda, MIT, and Konstantin Tsiolkovsky), creating the illusion of a reasoned and plausible logical chain.

The timing of the hoax played a large role in its success, coming as it did during the Glasnost period when the ebbing of censorship in the Soviet Union led to many revelations about the country's history, often presented in sensational form. Furthermore, Soviet television had, up to that point, been regarded by its audience as conservative in style and content. As a result, a large number of Soviet citizens (one estimate puts the number at 11,250,000 audience members) took the deadpan "interview" at face value, in-spite of the absurd claims presented.

Sholokhov has said that perhaps the most notable result of the show was an appeal by a group of party members to the Leningrad Regional Committee of the CPSU to clarify the veracity of Kuryokhin's claim, in response to which one of the top regional functionaries stated that "Lenin could not have been a mushroom" because "a mammal can not be a plant."

The incident has served as a watershed moment in Soviet (and Russian) culture and has often been used as proof of the gullibility of the masses.