The song is originally written for the Stephen King movie adaptation of the same name. The single became one of the Ramones' biggest radio hits, and a staple in their concerts during the 1990s.

King is a huge Ramones fan, and invited the band to his Bangor, Maine home as they played in New England. During the visit, he handed Dee Dee Ramone a copy of the Pet Sematary novel, and the bassist retreated to the basement. One hour later, he showed up with the lyrics to "Pet Sematary". Shortly afterwards, drummer Marky Ramone told that Dee Dee's attitude that day showed he could achieve his plans to leave the band and attempt a career at hip hop music. He likened Dee Dee to King, saying both wrote things people could relate because they "penetrated to the curiosity, fears, and insecurities carried around with them and couldn't put into words".

Producer Daniel Rey became a co-writer by helping the structure of the song, while producer Jean Beauvoir of the Plasmatics helped give the song a more commercial style fit for radio play and film inclusion. As "Pet Sematary" sounded closer to the rock ballads of the period, it was a struggle for Johnny Ramone to play the arpeggios and chords despite Dee Dee's guidance.

The music video for "Pet Sematary" was filmed at the Sleepy Hollow Cemetery in the eponymous New York village. Shot in a cold January 1989 night, the video features scenes from the film and the Ramones playing in an hydraulic platform placed inside an open grave, which was lowered until in the ending a horde covers the band in a "The Ramones" headstone. It was the last video featuring Dee Dee Ramone, which would depart the band and be replaced with C. J. Ramone. The video features cameos by Debbie Harry and Chris Stein of Blondie, and members of The Dead Boys.

...
Wikipedia