Hayao Miyazaki has stated that he prefers the French language cast (in particular Jean Reno as Porco Rosso) over the Japanese cast.
Hayao Miyazaki mentioned in a chat room that the ghost plane scene was inspired by a passage in a Roald Dahl story.
It was originally planned as a thirty to forty-five minute in-flight movie for Japan Airlines. Director Hayao Miyazaki eventually expanded it into a feature length production.
In the documentary The Kingdom of Dreams and Madness (2013), Hayao Miyazaki called this film "foolish". When asked why, he stated that it was foolish for him to make an adult movie for children.
Porco's hideout was inspired by Stiniva beach, a real beach on Vis island in Croatia.
Marco Pagot (Porco Rosso's real name) is named after an Italian animator who had worked with Hayao Miyazaki earlier in his career.
When Curtis tells Porco that Gina loves Porco, he punches the pig. As he does so, the left frame of Porco's glasses bends from a circle to a heart. It stays this way for the rest of the scene.
The song that Marco (Porco) is listening to on the radio in the beginning is "Le Temps des cerises" ("Sakuranbo no Minoru Koro" in the original soundtrack), which is the song Gina will sing in a later scene.
In the pirates' joint attack sequence you can read on the front part of one of the pirate planes: "Morte ai porcelli!!", Italian for "Death to the pigs!!"
The flying boats in Porco's World War I flashback story, are based on historical airplanes. Porco and his squadron are flying the Macchi M.5, an Italian single-seat fighter flying boat designed and built by Macchi-Nieuport at Varese. It was extremely maneuverable and agile, and matched the land-based aircraft it had to fight. The Austro-Hungarians are flying the Hansa-Brandenburg CC, a single-seat wooden-hulled fighter flying-boat, named CC after Camillo Castiglioni, financial controller of the Brandenburg company.
Originally planned as a comical in-flight short film. Due to the beginning of the Yugoslav Wars, Studio Ghibli developed the film into a feature length movie with a serious tone, while retaining the humor of the manga it was based on.
Some characters in the film are named after famous Italian pilots, Francesco Baracca, Adriano Visconti, and Arturo Ferrarin.
Porco Rosso is based on manga Hikoutei Jidai (The Age of the Flying Boat) by Hayao Miyazaki, part of Zassou Note series.
Marco Pagot, aka Porco Rosso, was possibly based on Ensign Charles Hammann, a US Navy fighter pilot during WWI. Hammann, like Porco, flew a Macchi M.5 biplane fighter over the Adriatic Sea against Austro-Hungary. He was awarded the Medal of Honor for rescuing, under fire, a fellow pilot who was shot down.
Hayao Miyazaki: [Ghibli] The name of the production studio (Ghibli) is embossed on the engine Piccolo installs in Porco's new plane.