The Los Angeles Police Department confirmed that someone stole the suit from a prop storage facility in Pacoima sometime between February and April 25.
VIDEO: Avengers movie magic at San Francisco's Cartoon Art Museum
The burglary was reported to LAPD on Tuesday.
The suit was the same costume worn by Downey Jr. in the first "Iron Man" film that jump-started the Marvel Cinematic Universe back in 2008.
Click here for a look at more stories and videos about Marvel.