The scenes with Oliver Barrett walking alone through a snowy New York were added after principal photography was completed. The production was almost out of money and did not have the necessary funds for permits to shoot in New York City again - so all the shots were grabbed illegally using a skeleton film crew and Ryan O'Neal.
In 1972, this movie was the most viewed film on television of all time.
Author Erich Segal wrote the screenplay first, then adapted this into a novel, which was published before the movie's release, and became a runaway bestseller.
To prepare for their roles, Ryan O'Neal learned to ice skate, and Ali MacGraw learned to play the harpsichord. When Arthur Hiller settled on Ryan O'Neal, he rehearsed the actor and Ali MacGraw for 10 days, because he wanted them to be friends before filming began.
Feature film debut of Tommy Lee Jones, a Harvard graduate several months before filming began. Erich Segal based Ryan O'Neal's character on Jones, and on his Harvard roommate, future Vice President Al Gore.