The Fault in Our Stars remains very true to the book. All the key plot points are in tact, and nothing really important is left out. At 2 hours, 5 minutes some things get compressed, a few characters are left out, and details are inevitably dropped along the way, but this is still an impressive adaptation.
But what was changed along the way? Let's take a crack at documenting the differences. We'll start with the most significant. [SPOILERS AHEAD!]
The Big Stuff
1. There's No Caroline Mathers
In the book, Hazel's relationship with Gus is complicated by his ex-girlfriend, Caroline Mathers, a cancer patient who died before the book begins. With her own death always feeling so near, Hazel can't help but compare herself to Mathers.
Mathers presence in the book serves mostly to deconstruct the myth of the strong and serene cancer patient, fighting to the end. Caroline's decline, as described through online updates, also prepares the reader for what Gus will soon go through. Her personality disappears as the disease progresses, finally taking her ability to speak before the end.
2. Gus' Decline Happens Mostly Offscreen
In the book, Gus' steadily declining health is plotted point-by-point until he's gone. Hazel sees him get weak, then stop walking, then confined to his bed. She helps clean him up after he wets his bed. She sees him move to a bed in the living room, only able to get out by wheelchair. The whole thing is excrutiating, but it gives you a real idea of what he's going through.
The movie version drops almost all this, but notably keeps the scene where Hazel rushes to a nearby gas station in the middle of the night after Gus decides he wants to be able to buy a pack of cigarettes for himself. The result is a little jarring. We miss some of the weight of Gus' decline, probably with the intent of keeping the movie from running too long.
3. There Was No Foreshadowing of Gus' Revelation
The book drops a few hints that Gus' cancer has returned, and none of them are in the movie. The big omission was Gus' fight with his mom. When Hazel and her mom go to pick up Gus on their way to Amsterdam in the book, they overhear an argument. Hazel hears Gus scream: “BECAUSE IT IS MY LIFE, MOM. IT BELONGS TO ME.” She thinks he's defending his relationship with Hazel, whose health is so obviously failing, but he's actually defending his decision to travel to Amsterdam in the face of his illness. In the movie version Gus arrives at Hazel's house in a limousine as if nothing is wrong.
4. There's No Kaitlyn
In the book, Hazel's connection to her old life, and the non-cancer world, is Kaitlyn, a high school girl who likes to speak in a faux-British accent and dish about boys. Kaitlyn's biggest moment in the book comes near the end when she helps Hazel figure out how to find Gus' final letter. The movie wisely cuts her out. (That whole manic pixie faux-Brit thing probably wouldn't work onscreen.) And in the process it puts Gus' final letter in Peter Van Houten's hands as he travels to Indiana, which makes a lot more sense narratively.
5. There's Only One Support Group Scene
It's a shame that Mike Birbiglia only gets a minute of screen time as Support Group Patrick, but really this seems like a wise move. In the book, the Support Group pops up occasionally to underscore what it's like to live with and talk about cancer. It's enlightening for the reader, but not really key to the plot.
6. Gus Doesn't Disappear in the Airport
As Gus and Hazel wait to board their flight to Amsterdam in the book, Gus disappears to grab something to eat, and doesn't come back until the plane is boarding, explaining that the line got super long. After boarding the flight, he admits the line wasn't very long, he just didn't feel like being stared at by people in the gate area. Was he embarrassed? No. He says the experience would have "pissed him off," and he didn't want to be angry on such a great day.
"That was the worst part about having cancer, sometimes: The physical evidence of disease separates you from other people," Hazel explains in the book. "We were irreconcilably other, and never was it more obvious than when the three of us walked through the empty plane, the stewardess nodding sympathetically and gesturing us toward our row in the distant back."
This is another scene that was cut for the sake of narrative flow, but in the book helps to underscore bigger points about the other-ness we assign to sick people.
The Medium-Big Stuff
7. We Don't See As Much of Isaac
Isaac's storyline gets dropped and picked up in slightly different places in the movie. Hazel doesn't visit a newly blind Isaac in the hospital like she does in the book. And she doesn't go over to his house and play audio-only video games with him after he loses his sight.
8. Gus' Half-Sisters Are Never Mentioned
As Gus' health declines in the book, his half-sisters, Julie and Martha, who are about 10 years older than him, arrive to help take care of him and to say goodbye. Since they don't really serve the story in any way, they're cut from the movie. In fact we don't see much of Gus' family in the movie.
9. Gus Says "I Love You" at Dinner
When Hazel and Gus go to dinner in Amsterdam, Gus says, "I love you," to Hazel, delivering pieces of his very quotable speech from the book in the process. In the book, this all happened on the plane before they landed in Amsterdam.
How could you not fall for someone who says this to you?
“I’m in love with you, and I know that love is just a shout into the void, and that oblivion is inevitable, and that we’re all doomed and that there will come a day when all our labor has been returned to dust, and I know the sun will swallow the only earth we’ll ever have, and I am in love with you.”
10. Amsterdam Isn't a Dreamlike Wonderland
In the book, Hazel and Gus arrive in Amsterdam in the spring, when the Elm seeds annually drop from the sky in what the Dutch call the "Springsnow." It turns the entire city into a kind of magical wonderland for them, especially when they're seated outside during their romantic dinner. (They're seated inside, surrounded by fake trees strewn with Christmas lights in the movie.) In the movie, the Elm seeds never make an appearance.
11. Cancer Genre Conventions Aren't Introduced Until the End
The Fault in Our Stars occasionally gets meta in the book, explaining young-adult cancer genre conventions within a young-adult cancer novel. Author John Green uses these digressions to further explain the gulf between how cancer patients are seen, and the lives they live. The only mention of genre conventions in the movie comes with Gus' "Last Good Day," as Hazel prepares to read Gus the eulogy she wrote for him.
12. The World's Saddest Swing Set Isn't Given Away
In the book, Hazel and Gus decide to give away her old swing set with an online ad titled, "Desperately Lonely Swing Set Needs Loving Home." In the movie, they just sit on it and look into each other's eyes.
13. There Are No "Existentially Fraught Free Throws"
In the book, Gus describes hitting 80 free throws in a row on his last day before losing the bottom half of his leg. Then, "All at once, I couldn’t figure out why I was methodically tossing a spherical object through a toroidal object. It seemed like the stupidest thing I could possibly be doing." He calls them "existentially fraught free throws," which Hazel, of course, loves. But they didn't make it into the movie.
14. Hazel Isn't a Vegetarian
In the book, Hazel explains to Gus that she's a vegetarian because she wants to "minimize the number of deaths" she is responsible for. This happens the first day they meet, and it's revisited only once, as they sit down to eat at Oranjee in Amsterdam.
15. The World Is Not a Wish-Granting Factory
In the book, Hazel and Gus, being precocious teenagers, share a few inside jokes. One of them is the recurring mantra that, "the world is not a wish-granting factory." The phrase only pops up in the movie once, when Gus tells Hazel that his cancer has returned.
The Small Stuff
16. They Never Watch 'V for Vendetta'
But Gus does have the poster on his bedroom wall.
17. Hazel and Her Mom Don't Celebrate Half Birthdays
18. Not As Much Video Games
Gus plays a lot more "Counterinsurgence" in the book, making a point of sacrificing his character in heroic ways to save the lives of hostage children.
19. Hazel and Gus Watch 'Aliens' on the Plane to Amsterdam Instead of '300'
20. Hazel Doesn't Have a Sick Day When They Arrive In Amsterdam
It probably would've killed the momentum of the movie.
21. Peter Van Houten Isn't Fat
But he is Willem Dafoe, which seems like a win.
22. Hazel and Isaac Deliver Their Gus Eulogies in the Church Itself
As opposed to the basement, aka "The Literal Heart of Jesus."
23. Gus' Funeral Service Is in the Cemetery
In the book, Hazel leaves his service at the church early and heads to the cemetery for the interment. The movie gets it all done in one place.