According to Michael Crawford, he auditioned for Gene Kelly in his hotel room. Kelly asked him if he knew any tap steps, and tried to coach him on some on top of the coffee table. Crawford tried to imitate him, but was so nervous at the idea of dancing with the famous dancer and choreographer that he kept messing up. He was convinced he'd failed the audition, when Kelly told him "What we're looking for is an attractive idiot: My wife thinks you're attractive, and I think you're an idiot!", telling him he'd gotten the part.
On a break from filming, Walter Matthau and Michael Crawford visited a nearby racetrack and saw a horse named Hello Dolly. Matthau refused to place a bet on it because it reminded him of Barbra Streisand, whom he detested. Crawford placed a bet on the horse. It won the race, and Matthau refused to speak to Crawford for the rest of the shoot unless absolutely necessary.
This was one of the first films released on home video (VHS and Betamax) in the US. It was released in fall 1977 by the Magnetic Video Corporation, one of the 50 original films it licensed from Fox. Its catalog number was CL-1001.
Louis Armstrong's final film. He was on set for half a day, and filmed all of his shots in one take. In 1964, his recording of "Hello, Dolly!" hit #1.
The facade of the Harmonia Gardens still stands as of 2010 on the 20th Century Fox lot, though the park across the street is long gone.