Actually, there’s some historic fact to back this up. Apparently he lost it during WWI.
Couldn’t happen to a nicer guy. 
LINK TO COLUMN: Did Hitler have only one testicle? - The Straight Dope
Aw, nuts. I mean, nut.
You know who else has only one testicle?
Armstrong!
Still controversial. Probably never to be proved.
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Well, then, Mr. Perfect, let’s blow off one of your testicles in a World War, and we’ll just see how YOU start treating the Jews, and Poland, and the gypsies!!!
I feel compelled to include this quote from the linked article:
*
In 2002, controversial artist Takashi Murakami made a commissioned sculpture of Hitler’s testicle for an unnamed bidder for an alleged $14.7 million. The testicle was rumored to have a diameter of 10 feet and was made of cast iron. Art critic Brian Sewell called the work “feeble”.*
Himmler had something similar.
And poor old Goebbels had no balls at all.
If there has ever been an inappropriate adjective for anything that is made of cast iron with a diameter of ten feet, it would be “feeble”.
Apparently its been reported that a medical report was unearthed documenting Hitler having only one testicle (http://forward.com/news/breaking-news/327563/hitler-had-just-one-testicle-medical-records-show/)
The Sun? Really? The Sun? The bloody SUN?
Zombie outrage.
In fact a modern day ink pen company adopted his nickname “Uniball”.
Hitler was born with only one according to a prison doctors record. I’ve always heard this about Hitler and apparently documentation has turned up that confirms it wasn’t just a rumor. Crytorchidism is when one has wondered off, not descended, vanished, it simply means only one ball is where two should be.