Police are appealing for witnesses after a fight in Catterick Garrison in the early hours of Sunday.
The incident happened near to Louis Bar on Kitchener Road at around 4.40am involving a large number of people and which left a man seriously injured.
He was taken to James Cook University for treatment.
A 22-year-old man was arrested in connection with the incident and released under investigation while enquiries continue.
A spokesman for North Yorkshire Police said: “We are requesting the public’s assistance to help establish the full circumstances surrounding the incident.
“In particular, officers would like to speak to a group of men who were dressed in fancy dress outfits who may be able to provide important information.”
Anyone with information that could assist the investigation should contact North Yorkshire Police on 101 and speak to the Force Control Room.
If you wish to remain anonymous, you can pass information to Crimestoppers on 0800 555 111.
Please quote the North Yorkshire Police reference number 12180233261.