During Miles' interrogation of Uncle Buck (22:36 to 23:01), John Candy wrote out the script's dialogue, and wore it atop his head so Macaulay Culkin could read the lines more quickly, and keep the pace of the scene very fast. (Note that this would be the take of the scene when the camera was set for close-ups of Miles.)
One night during filming, John Candy went to a bar with Music Supervisor Tarquin Gotch, and spent most of the night there meeting people. The next day, John Hughes heard a caller on a radio talk show excitedly describe his evening with Candy. Hughes was upset with Candy, and despite Candy's assertion that Buck was supposed to appear disheveled, Hughes cancelled his scenes for the day, and told him to get himself together and get some sleep.
John Goodman was considered for the role of Uncle Buck, he would later go on to play Fred Flintstone in The Flintstones (1994), a role, for which John Candy was also up, as The Flintstones (1960) was his favorite cartoon, sadly his premature death in 1994 prevented this.
The movie was originally intended to be shot in the St. Louis area, rather than John Hughes' traditional Chicago. Filming was about to begin, when the decision was made to move the shoot to Chicago (the reason being, that the film was set in winter, and the winter of 1988 was unseasonably warm in St. Louis, leading to the change).
When Buck goes to the party to find Tia, he hears rap music playing ("Bust a Move" by Young MC), and jokingly says "Who's that? The Grass Roots?" The Grass Roots were a popular band in the late 1960s, that had a string of hits, including "Lets Live For Today", "Midnight Confessions", and "Temptation Eyes", amongst others.
When casting the role of Kevin McCallister in Home Alone (1990), Chris Columbus had already seen Macaulay Culkin in Uncle Buck (1989) but he wanted to audition some other kids first even though John Hughes had his heart set on Culkin. So Columbus met Culkin in New York and was very charmed by him and he thought he was fantastic. Columbus auditioned five other kids and none of them shaped up to Culkin. Columbus went with Culkin because he was not as picture perfect and he had an instant bond to the kids in the audience. Columbus knew the cameras would love him and he was immensely funny.
Uncle Buck asks Miles, who is interrogating him, "What's your record for consecutive questions asked?" Miles replied, "38". John Candy was thirty-eight-years-old at the time this movie was being filmed.
Variety describes John Candy (who plays uncle Buck) humorously as follows: Unfortunately, Candy is too likable to give the role any edge. When called upon to be tough or mean he's unconvincing, as in the slapstick dealings with the precociously oversexed boyfriend Bug (Jay Underwood) of eldest daughter Jean Louisa Kelly.
Gaby Hoffmann, Amy Madigan, John Candy and Laurie Metcalf have co-starred in films with Kevin Costner. Hoffmann and Madigan in Field of Dreams (1989) - interestingly released in the same year as Uncle Buck - and Candy and Metcalf in JFK (1991).
One of two films released in 1989, that star Gaby Hoffman and she has a co-star with the surname Brown. In this film it's Garrett M. Brown. The other film is Field of Dreams, in which Hoffmann co-stars with Dwier Brown.