Ron Kovic, a Vietnam veteran, wrote Born on the Fourth of July in 1976 as both an autobiography and an anti-war manifesto. He was paralyzed in the war and became an activist. Tom Cruise played Kovic in the 1989 film version directed by Oliver Stone. Kovic co-wrote the film with Stone, so it follows the facts of his life and the narrative of the book fairly closely.
Because of this, the major differences are in changing of characters and events to increase drama; for example, Kovic never confessed his (possible) role in a soldier's accidental death to his parents and wife. His reasons for going to war were changed from (book) his love of glamorous war films to (film) making his parents proud, and while in the book Kovic mentions the horrible treatment of veterans in hospital, in the film he meets a specific anti-war activist who inspires his later work in the field. There are also minor events that are glossed over or skipped, and the timeline is shortened (as is typical) because the film must be a certain length. Overall, though, the involvement of Kovic in the film makes it one of the more accurate film adaptations.