During an interview, it was revealed that Sarah Jessica Parker and Kim Cattrall loathed each other since the first season. The relationship became even more strained when Parker was made producer; their on screen friendship was so well done that fans had no idea. This is why whenever the four women appeared at events, Parker and Cattrall were opposite each other. Both women felt it was "unprofessional" to bash each other during the series' run.
The medicine cabinet in Carrie's apartment was first spied by Sarah Jessica Parker at a flea market shortly before filming began on the series. She and Matthew Broderick didn't buy it but reconsidered. When they went back, the cabinet was already sold to "some TV show". When she showed up for filming, the medicine cabinet was there.
From the very first season up to the 12th episode of the 4th season, in the opening credits, Sarah Jessica Parker's name was shown with the World Trade Center towers behind her name. After the terrorist attacks on the USA of 11 September 2001 and the collapse of the towers, her name then appeared with the Empire State Building in the background. The same thing happened with the show's main title.
Sarah Jessica Parker had a clause in her contract for this show stipulating that she will not do any full nudity. This is why the audience never sees Carrie in anything less than underwear whereas all the other main female characters have been filmed in much less.
"Jules & Mimi," the bi-racial sexually charged BBC series that Miranda recorded and watched religiously on her TiVo, is not a real show. Paul Lee, CEO of BBC America, quipped to Jack Myers Report, "We should commission Jules & Mimi. It would be the first time a scene in a sitcom has inspired another show."
Showrunner Michael Patrick King admitted that one of the main reasons behind the love story between Carrie and Aleksandr Petrovsky is that he was sick of the fans complaining of how Big was older than Carrie, so he decided to pair her up with a real older guy.
The part which ultimately went to Matthew McConaughey in the Episode 'Escape from New York' was originally written for Alec Baldwin who declined. The producers then contacted George Clooney who, although was interested in it, couldn't do it. The script was then sent to Warren Beatty who also declined.
The exterior used for Carrie's apartment at 64 Perry Street, which is actually a 4,000 square foot five bedroom townhouse, was sold to anonymous buyers in 2012 and again in 2013 for $9.85 and $13.25 million respectively.
Samantha is the only one of the four leads to never have a family member make any kind of appearance in the series. Family members of Charlotte and Miranda appeared, and Carrie's father is shown once in photographic form.
Although Carrie says her address is 245 E. 73rd Street in Manhattan, the actual exterior of her iconic brownstone apartment is 64 Perry Street in the West Village. You can visit the apartment, but a chain blocks people from going up the steps as it is a private residence.
The trivia item below may give away important plot points.
Michael Patrick King during a commentary of the third season stated the reason why he did not want to bring much of the 4 main characters families into the show was to maintain the focus being centralized on the four leads. In fact, when Charlotte gets married the first time her father's face is barely even shown as he walks her down the aisle.