During filming, Williams had to sit in the makeup chair for 4 ½ hours every day in order to become Mrs. Doubtfire.
When Miranda gives the Hillard's home address to Mrs. Doubtfire over the phone, she names the actual address where the movie was shot: 2640 Steiner St.
The icing melting off of Mrs. Doubtfire's face was completely unintentional. The set lights were very hot, and it unexpectedly began dropping from his chin. Williams went along with it and improvised the majority of this scene.
Robin Williams says the word "dear" 101 times throughout the film. Sometimes he says it clearly, and sometimes it's more of a mumble. You have to listen very closely to hear all 101.
Director Christopher Columbus always had two to three cameras surrounding Robin Williams. This was because Williams was famous for spontaneously improvising and the camera crew never knew what he would do next.
While the movie was being filmed, Sally Field was going through a breakup with Burt Reynolds. Not only that, but Robin Williams would later go on to divorce his wife and marry his nanny (as opposed to divorcing his wife and becoming the nanny in the film).
Tim Allen was originally offered the role of Daniel Hillard/Mrs. Doubtfire but turned it down. He was also offered the role of Stu Denmeyer, but the role ended up going to Pierce Brosnan instead.
Blake Lively auditioned for the role of Natalie Hillard, the youngest Hillard child. She lost the role to Mara Wilson.
Mrs. Doubtfire was Mara Wilson's film debut.
Mrs. Doubtfire is based on a British novel by Anne Fine. Allegedly, there was a store the author would regularly walk by that sold jewelry and old furs. The shop was owned by a woman named Madame Doubtfire.
When Sally Field was drinking a cappuccino on set, she accidentally got a cappuccino moustache on her upper lip. The producers loved it, and decided to put it into the movie.
Lisa Jakub, the actress who played Robins' eldest daughter Lydia, was kicked out of her Toronto school for taking a five-month-long hiatus to film the movie. Robins personally sent a letter to the school asking them to reconsider their decision. The school framed the letter, but they didn't reconsider their decision.
When Mrs. Doubtfire's teeth fall into a wine glass and she proceeds to fish them out she says, "Carpe Dentum...seize the teeth." This was a reference to Dead Poets Society in which Robin Williams famously says, "Carpe Diem...seize the day" to his students.
Robin Williams walked into an adult shop dressed as Mrs. Doubtfire to test the believability of his character. No one recognized him until he went up to buy a toy.
When Robin Williams passed away, grieving fans visited the San Francisco home where Mrs. Doubtfire was filmed. This is the front doorstep shortly after his passing.