The 5,000 Fingers of Dr. T (Original Cut of Dr. Seuss Movie; 1953)
The 5,000 Fingers of Dr. T was the only film written by Theodore Geisel, better known as Dr. Seuss.
The film itself is not lost. However, the original cut of the film, which had a darker tone and included twice as many musical numbers, is completely lost, as even Sony Pictures hasn't been able to find a copy of it. However, the screenplay has been found, which is 1000+ pages in length (and far longer than an average movie screenplay), but has not been released.
Before his death, Geisel denounced the film and purposely left it unmentioned in his biography, so he may have played a part in its disappearance.
The film's story focuses on Bart, a young boy living with his widowed mother. More than anything, Bart dreads his strict piano instructor, Dr. Terwilliker. After Bart complains to the plumber, August Zabladowski, about how his instructor might be influencing his mom, Bart dozes off at the piano and dreams.
In his dream, he finds himself trapped in the Terwilliker Institute, a place where Bart's piano teacher is a dictator. Dr. Terwilliker has created a piano so massive that it requires 500 boys, including Bart, to play it, enslaving them in the institute. Bart's mother, hypnotized by Dr. Terwilliker, believes she is his bride-to-be. Throughout the film, Bart tries to save his mother by evading guards and recruiting the reluctant Mr. Zabladowski to help him. After convincing the plumber to help, the two build a machine that ruins the debut concert for the mega-piano and starts a riot for the enslaved boys. Eventually, the machine explodes, waking Bart from his dream. Noticing when he wakes up that the plumber has distracted his mother, Bart runs outside to play.
Many changes were made to the film prior to its release due to negative feedback from the test audience; 11 musical numbers were removed entirely from the production, leaving 13 in the movie. Prior to their removal, every musical number had been filmed. It's unknown if the footage survives to this day or if any non-musical delete scenes were filmed.
Some censorship was also added to one number, namely the mention of "gas chambers" in "The Elevator Song", which could have been misconstrued as a reference to the Holocaust, so the specific stanza was removed.
While neither the screenplay or any of the cut footage is available, all of the songs cut from the film can still be heard on the film's musical soundtrack.