Hello, Dolly! is often thought of as having a been a huge flop at the box office. In fact, it was one of the highest grossing films of the year it was released. Because its production cost was so high — usually said to have been $25 million — it managed to be one of the highest grossing films of the year and to still have lost a bundle for the 20th Century Fox. Because of the way film rentals work and because of the costs of advertising, it was usually estimated at that time period that a film needed to gross two-and-a-half times its production cost to break even. On its initial release, the film grossed $33 million. So while it was a disaster for the studio, it was actually popular with audiences. Just not nearly popular enough.
Gene Kelly did not want to direct the film. He was at odds with Michael Kidd through much of the production. And the budget grew too big for Kelly to handle. All of this resulted in a very difficult shoot.
Fox couldn't release the film until they went to court with David Merrick.
Walter Matthau grew extremely impatient with Barbra Streisand during the filming. Eventually, he refused to be around her except when filming scenes together. He is quoted as saying that she "had no more talent than a butterfly's fart".