World War Z is the first that sprang to my mind.
The Lawnmower Man. Stephen King sued the studio to have his name removed from the movie because it bore absolutely no relation to his short story. He won.
The Spy Who Loved Me. Ian Fleming himself described the book as “a failed experiment”. When he sold the movie rights, he told them to use the title, and re-write everything else. They did.
In Octopussy, the entire plot of the short story is summarized in about 30 seconds of dialog between Bond and Octopussy. In The Living Daylights, the short story became the pre-credits sequence of the movie. In The Man with the Golden Gun and Moonraker, only the names of the villains made it into the movies.
Logan’s Run has three scenes where events and dialog are copied near-verbatim from the book. But the rest of the movie is very different.
One of the few movies I ever walked out on (and I sat through Slithis) was
H. G. Wells' The Shape of Things to Come - Wikipedia.
I still don’t know how the title of the movie didn’t constitute copyright infringement or outright fraud.
The short story “Quantum of Solace” is about James Bond and a couple of rich toffs gossiping at a restaurant. The movie is not.
RED, the comic book miniseries, was a gritty action thriller. The main character was a retired CIA assassin. As part of a housecleaning operation, and to cover up past crimes, a new CIA DDO orders him killed. It does not go well. The comic makes a big deal about the Cold War era CIA, which Got Things Done, even if they were awful things, while the then-current CIA has been taken over by feckless political operators. The Retired Extremely Dangerous assassin Jason Bournes his way through to the DDO, and it’s not so much that he’s a super badass, although he is, as that the current CIA has just gotten too soft, and they just don’t have any proper “hard men” anymore.
The Bruce Willis movie, “RED”, is an action comedy, about a retired CIA assassin who saves a pretty, and disturbingly younger, pension administrator that the CIA for some reason decides to kill, along with him. He also teams up with several other retired spies to teach these young folks a thing or two.
A couple of characters have the same name, and they kept an element of the original premise, of a Retired Extremely Dangerous CIA assassin being targeted for death by a new CIA administration, but other than that…
Really, the Jason Bourne movies were much closer adaptations of the RED comic book than the RED movie was. For that matter, the Jason Bourne movies were probably closer adaptations of the RED comic book than they were of their own source material…
Well, at leas the first had actual vampires. 
I would add Blade Runner, and Total Recall is much more like Overdrawn at the Memory Bank than it is We Can Remember It For You Wholesale.
I actually preferred the movie ending of The Natural, but it is 180 degrees away from the novel.
I’ll go there.
Starship Troopers Other than some character names and a couple of minor plot points, the movie bears absolutely zero relation to the book. Or the book’s intent.
Except for The Hunt for Red October, none of the Tom Clancy adaptations I’ve seen come close to the book. I stopped going to them after the Arab terrorists in The Sum of All Fears became Neo-Nazis instead.
When I read The Great Escape, I was surprised by how different it was from the movie. I realize they weren’t filming a documentary and still got most of the technical details right, but parts of the film are so unrealistic I have to suspend my sense of disbelief when I watch it nowadays. I find myself asking all sorts of questions, like “What would they do with a prisoner who assaulted a guard in plain view and then escaped and killed a German soldier in order to take his motorcycle?”
In the book, a prisoner was shot just for standing in a doorway to watch bombers going overhead.
Adaptation has already been mentioned–the movie only uses the book’s real story as a bare framework for the antics of Cage’s crazed Kaufman twins. Susan Orleans’ tale of John LaRoche and his obsessions could’ve made an good (but entirely different) movie on it’s own without the whole Kaufman story line.
The Steve Martin movie Cheaper by the Dozen has basically nothing to do with the book by Frank and Ernestine Gilbreth that it’s based on.
Another adaptation of Stephen King to add to the list: The Dark Tower doesn’t bear much resemblance to collected volumes or any one of its constituent books.
Sorry. I was not clear in post 18 that Hopscotch is the English translation of (Spanish) Rayuela.
I also meant “based on a play or novel” in the OP, but everyone seems to understand what was meant. Thanks!
Shocked that the Wizard of Earthsea adaptation hasn’t been dropped in yet. The most notable change was the lead character’s race/skin color, then it just got worse from there. Ursula LeGuin was pretty disappointed with the (pathetic) effort.
The Scarlet Letter 1995. Hester, Dimmsdale and their tyke literally ride off into the sunset.
The Secret Life of Walter Mitty, the 1947 film starring Danny Kaye. (I know nothing of the 2013 film.) The original James Thurber short story was little more than some vignettes of Mitty’s daydreams following his life for one day. There was really no story there.
The movie included most of those, but greatly expanded upon that by adding an actual story line, in which he gets mixed up with a woman trying to secure some Dutch treasures hidden from the Nazis by the Resistance during WWII and a gang of hoodlums trying to steal the same, who attempt to gaslight Mitty to the point of doubting his own sanity.
The movie essentially had everything that the short story had, plus a real story and more. I enjoyed it very much, and I recommend it. Danny Kaye was exactly the right actor for the part. (I believe there are some excerpts up on YouTube.)
To be sure, the movie was a parody derived from the book, so one would expect it to be very different.
In general, parodies keep very close to the original (cf. Bored of the Rings, Harvard Lampoon Life Magazine parody, or any classic Mad Magazine parody). The entire point of a parody is to mimic the original.
One Flew Over The Cuckoo’s Nest, the 1975 film starring Jack Nicholson as McMurphy and Louise Fletcher as Nurse Ratched, disappointed me.
In the book, Chief Bromden was a central character, and the narrator of the entire story from beginning to end, as seen through his PoV. But Bromden was thoroughly totally psychotic, living in a bizarre world of nightmarish delusions and hallucinations, so he was far from a reliable narrator.
A central theme of the book was his character development (including development of Bromden’s biographical history), and his interactions with McMurphy, leading him to gradually become more-or-less sane towards the end of the book, and leading to his escape. As he gradually regains his sanity, his narration becomes more and more reliable. (Determining which details of his narration are real and which are just his delusions is left as an exercise for the reader.)
All this is entirely lost in the movie. Bromden is reduced to a mostly incidental character in the background, playing hardly any part in the story. The critical scene where he votes with the others to have the boating field trip, and discovers that he has some autonomous agency, to omitted completely.
The entire boating field trip misses everything that mattered in the book, and in particular the political battle between McMurphy and Ratched leading up to the trip is entirely omitted. In the book, they have a battle of wills trying to influence the others to vote for or against the trip. In the movie, it was just a spontaneous prank in which the inmates escape and go commandeer a boat.
This continues in later Jack Ryan/Clancyverse productions. The show on Amazon will take moments from the novels and re-frame them (so for example the gunfight at the beginning of Patriot Games happens in a totally different context at a gas station in France) and has little use for plots, characters or characterization (looking at you in particular Cathy Meuller!) from the books. I find that as an adaptation it is distractingly bad and I have to try to enjoy it as a straight spy thriller with some in-jokes for Clancy superfans.
Without Remorse was also very, very different from the source material. It keeps the basics of the plot - John Kelly wants revenge. But that is about it. It does not follow the plot of the book at all. Doesn’t even try to. And the mention of Rainbow at the end tells us that if there is more to come, it will also skip over about twenty years of Clancy’s work.