Blooper: During Romeo's shootout with the cops just outside the Capulet mausoleum, his P-13 turns into a Beretta 92FS Inox.
Breakaway Pop Hit: The soundtrack exposed a few songs, most notably The Cardigans' "Lovefool" and the choral version of "Everybody's Free (To Feel Good)" (nowadays known as "Wear Sunscreen").
Originally, the 14-year-old Natalie Portman was cast as Juliet, but the director thought that the much older Leonardo DiCaprio looked like he was "molesting her", so the 16-year old Claire Danes was hired instead. Danes was only three years older than Juliet.
Leonardo DiCaprio was 21 when he filmed this. Assuming Romeo's friends are supposed to be of similar ages to one another, keep in mind that Harold Perrineau (Mercutio) was 33.
Fake Nationality: Claire Danes and most of the actresses who were considered for Juliet were all very white. Odd when you realize that the Capulets were very obviously meant to be a Latino family, or at the very least a Latino/Italian mix.
Could be a case of unintentional Fridge Brilliance since the Italian mix could explain why Lord Capulet and Juliet are played by white actors (Paul Sorvino is of Italian heritage while Claire Danes is of Anglo and German heritage) so Juliet could be half-white and half-Latino, with Lord Capulet being white (Italian) or alternately, Lady Capulet is a white Latina (i.e. mostly European Spaniard descent) or is mixed ethnicity herself, given she is depicted as a dark-skinned blonde.
Hostility on the Set: Leonardo DiCaprio and Claire Danes did not get along during filming. Danes felt that DiCaprio was a nuisance and "very immature" because he pulled pranks on crew members and generally had a "goofball attitude." DiCaprio felt that Danes was stuck-up and too serious. Tellingly, they rarely spent time together off-set.
After Friar Lawrence suggests the marriage idea Romeo starts to run out of the church and crashes into a lamp. This was a genuine accident that was left in as it added to the energy of the scene.
The Dramatic Wind during Mercutio's death scene were actually the winds from a hurricane that was approaching the beach where they were filming (which ultimately destroyed the entire Sycamore Grove set). The actors agreed to go out and film the scene, even though it meant getting sand blasted into their faces.
Marlon Brando expressed interest in playing Father Laurence, but personal family problems took him out of the running.
Claire Danes and DiCaprio were going to be reunited in Titanic (1997), but Danes was too tired after shooting, so the part of Rose went to Kate Winslet instead.
The song "Come What May" was written for this film but ultimately not used. Baz Lurhmann would later use it in Moulin Rouge!, but it being intended for an earlier film rendered it ineligible for Best Original Song at the Oscars.