The pilot of a plane had to shout a warning to his co-pilot after spotting a UFO, says a report.
The incident happened in 1991, when the pilot of an Alitalia plane shouted "Look out!" after spotting what he said was a brown, missile-shaped object.
It was investigated by officials, but even though they didn't work out what it was, they closed the inquiry.
The sighting was in one of 19 files created between 1986 and 1992 that have only just been published.
That sighting isn't the only one of a similar sort of object - there are others referring to a "wingless projectile" or black "lozenge".
The Ministry of Defence is in charge of the UFO files, and the documents that have just been made available belong to them.
The files are being held at a place called the National Archives in Kew Gardens in London, which is a big store of important documents.