Originally titled "Maharishi", the Beatles changed the title to "Sexy Sadie" to avoid the potential for litigation as the song's lyrics portray the Maharishi Mahesh Yogi in a less than favourable light. Lennon was disillusioned after the Maharishi had allegedly made a pass (sexual advance) at one of the female members of their entourage, though in later years George and Paul endeavored to set the record straight. Lennon once said of the song: "That was inspired by Maharishi. I wrote it when we had our bags packed and were leaving. It was the last piece I wrote before I left India. I just called him, 'Sexy Sadie,' instead of (sings) 'Maharishi what have you done, you made a fool...' I was just using the situation to write a song, rather calculatingly but also to express what I felt. I was leaving the Maharishi with a bad taste. You know, it seems that my partings are always not as nice as I'd like them to be.
After returning from India John scratched the lyrics into a piece of wood, with the original title "Maharishi". The recorded version changed only after George insisted that if the song was used he wanted the name changed and persuaded John to change the title to Sexy Sadie. George recounts the event in the directors cut, from the anthology film. Derek Taylor remembered John fiddling about scratching the wood in the Apple offices. The wood ended up in the possession of Maureen Starkey and was ultimately sold to a Beatles collector.
In a 1969 interview, John Lennon stated one of his favourite songs was "I've Been Good To You" by Smokey Robinson & The Miracles. The Miracles song begins with the line Look what you've done / You made a fool out of someone, compared to Sexy Sadie's What have you done? / You made a fool of everyone.
As described in Vincent Bugliosi's Helter Skelter, Charles Manson took the title of this song as a reference to Manson Family member Susan Atkins, who was nicknamed Sadie Mae Glutz, prior to the release of the White Album.
Songs deemed similar to "Sexy Sadie" include Australian rock group Jet's "Look What You've Done", which has similar (occasionally identical) lyrics and style to the song. Oasis lifts a remarkably similar intro on their b-side, "Sitting Here In Silence (On My Own)." Also, Jack Johnson's song, "Cocoon" (from the On and On album), is strikingly similar to this song and parts of the piano are similar to Radiohead's song "Karma Police", and the band has apparently acknowledged the similarity.