According to one biography, Robin Williams decided to test out the believability of his Mrs. Doubtfire character during filming by going, as Mrs. Doubtfire, into an adult bookstore and making a purchase. He was able to do so without being recognized.
During the scene when Mrs. Sellner comes to inspect Daniel's apartment and Daniel/Mrs. Doubtfire is serving her tea, the icing on his/her face is melting off. This was not intentional. The heat from the set lights melted the icing on his face and Robin Williams improvised the bulk of that scene.
Chris Columbus would use two or three cameras at a time, when shooting Robin Williams' scenes, uncertain of what the famously improvisational actor would come up with. Columbus viewed shooting these scenes as if he were making a documentary film.
Known for his trademark spontaneity of improvisation, Robin Williams was given free range by director Chris Columbus to do what he needed. However, his improvisation can occasionally spark off numerous references to other works that prove to be legal headaches for movie studios. The scene where Daniel speaks with his wife and refers to her clothes as "this lovely Dances with Wolves (1990) motif", required legal clearance for the studio to put it in the film. Associate producer Paula DuPré Pesmen later kept track of every reference Williams made while improvising.
Talk of a sequel began in 2003, with a script being written by Bonnie Hunt. Robin Williams was set to return in disguise as an old nanny like in the first movie. Due to problems with the script, re-writing began in early 2006 as Robin was allegedly unhappy with the plot. The film was expected to be released in late 2007, but following further script problems, the sequel was declared "scrapped" in mid-2006. The sequel's story was originally said to involve Williams, as Mrs. Doubtfire, moving close to his daughter's college, so he could keep an eye on her. Serious discussions regarding the sequel re-ignited in April 2014, with an announcement that Robin Williams and Chris Columbus would be teaming up with Fox2000 to produce the sequel. Williams' sudden death, just four months later, in August 2014 ultimately sealed the project's fate once and for all.
In the pilot for Charmed (1998) toward the end of the show, Shannen Doherty picks up a newspaper from the sidewalk. The newspaper headline reads "Firemen Doubt Fire was Accidental", the same newspaper prop used by Robin Williams's character giving him the idea for the name "Mrs. Doubtfire".
Robin Williams used much of his real childhood nanny to characterize Mrs. Doubtfire. When British tabloids found this out, they went looking for his former nanny. They found his real nanny, "Lolly", in a Michigan nursing home, and the reporters and photographers flocked to the little town to get an interview with her. Lolly balked at the attention and downplayed her impressive role. (The reporter found out Lolly had in fact been a nanny to other Hollywood celebrities, including Mr. and Mrs. Lyle Waggoner.) As a result, the local newspaper ran a story of Lolly with the heading "The Real Mrs. Doubtfire".
Harvey Fierstein had seen and been impressed by Robin Williams's impersonation of him on Comic Relief. He heard through friends that Williams would be playing a character with a gay brother, and approached him about playing the part.
Stu was originally scripted to be an arrogant villain but Chris Columbus felt that it hurt the relationship with Mrs. Doubtfire so Stu was re-written to be more the perfect potential replacement for a father for the kids.
According to Chris Columbus, the film was initially going to be set in Chicago. But, after checking out San Francisco, they chose to set the film there. Columbus had been living in New York City for years, and was in need of a change of scenery to raise his family. During filming, he and his family had been so taken with the city, that they settled in San Francisco after the film was completed.
While extracting the false teeth from the wine glass, Mrs. Doubtfire jokes "Carpe Dentum... seize the teeth." This echoes "Carpe Diem... seize the day", Robin Williams' recurring phrase from Dead Poets Society (1989). Coincidentally, Williams had earlier appeared in the little-known movie Seize the Day (1986).
When the family is looking for Mrs. Doubtfire's replacement, many of the potential nannies are members of the crew, including production assistant Erik Ross, art department coordinator Kristen Ross and production coordinator Jacqueline A. Shea. The final name crossed off the list is that of associate producer Paula DuPré Pesmen.
One of the makeup attempts winds up looking more like an old Jewish man. Robin Williams improvs on this for a moment, then Williams, Harvey Fierstein, and Scott Capurro sing the chorus of "Matchmaker, Matchmaker", from 'Fiddler On The Roof'. Fierstein has starred in 'Fiddler' in two different Broadway revivals.
When Anne Fine was approached to make a movie out of her novel, her original choice for the lead role was Warren Beatty. Because of Beatty's reputation as a great womanizer she thought it would be hysterical to see him dress up and pretend to be a woman.
Polly Holiday's character of the Hillard family's next door neighbor Gloria Chaney, was originally scripted as a large supporting character and had a much bigger role in the film. Many scenes were filmed in which Daniel as Mrs. Doubtfire gets even with Gloria as Gloria tells Mrs. Doubtfire that she heard rumors that Daniel cheated on Miranda and abused his children. This leads Daniel as Mrs. Doubtfire, observing Gloria's passion for gardening, to give Gloria a formula that will help her flowers bloom better, and the secret ingredient in the formula is dog urine. Several scenes show Gloria actually getting dog urine and applying it to her flowers which kills them, and upsets her very much. Due to time constraints all of these scenes were cut out, and as a result, in the final cut of the film, the character of Gloria is only seen once during the opening credits before she calls Miranda to complain about Daniel throwing a birthday party next door, and later right before Daniel/Mrs. Doubtfire, rips the logo off of Stu's Mercedes Benz, you can see a brief glimpse of Gloria doing some gardening. All of Gloria's deleted scenes can be seen in the special features on the film's DVD.
According to some rumours, it's been suggested parts of the story were originally intended for a potential plot of a film version of the TV series of Home Improvement (1991) at the time. With the story being Tim getting divorced with Jill and being forced to pretend to be a 60 year old nanny in order to spend time with the kids. It's been said the reason for this not happening was because both Tim Allen and Patricia Richardson both hated the idea plus didn't feel Home Improvement needed a film version.
Daniel Hillard's career as a voice actor is unusual, being that he is based in San Fransisco (not known as a key hub of voice-over work) and we see him providing full voices for finished animation (extremely rare in American VO traditions). This could be considered a mistake, but it could also be assumed that Daniel is replacing a voice track that is for some reason faulty, and must do the entire track over in an automated dialogue replacement session. This could be why the voice director points out how much money the session is costing the studio.
The animation director who scolds Daniel for wasting the studio's money at the beginning of the movie is played by Terence McGovern. Terrence McGovern lends his voice to animation often, most notably as Launchpad McQuack for DuckTales (1987) and Darkwing Duck (1991). McGovern is a native of Berkeley, CA and a former DJ and radio personality at KSFO radio in San Francisco.
When Miranda's boss played by Martin Mull, towards the beginning of the movie stated that Stu wanted to invest millions into the Wellman Mansion. Martin Mull played on Roseanne where Roseanne and Jackie (Roseanne's sister) worked for Wellman plastics during the early seasons of the show.
During the conversion to film, most of the characters were moderated heavily. In the book, all the main characters, apart from Natalie, tend to act in self-interest and expect a large amount of credit whenever they do otherwise. The divorce of Miranda and Daniel in the book is also much more bitter.
Toward the end of the movie when Mrs. Doubtfire is filming her television show, the mailman who comes to the door can be heard saying he has a letter from Katie in Youngstown, Ohio. Director Chris Columbus is from Youngstown, Ohio.
The trivia items below may give away important plot points.
The producers fired the original screenwriter because of an "unhappy" ending, where the parents do not get back together. After several re-writes, with a different, "happy" ending, they realized that the original ending was, in fact, better. They re-hired the original writer and went back to the original ending.
Mrs. Doubtfire is quietly singing "The Crying Game" as she walks up to Stu's Mercedes (the scene where she pulls the hood decal off). The song is the theme from The Crying Game (1992), a movie that became famous (or notorious, depending on the viewer) for its surprise plot line about a trans-gender woman.