The man suffered a fractured skull and jaw during the assault in Armagh.
Detective Chief Inspector Stephen Wright explained: “Around 6pm on Wednesday, 7 January, we received a report of a man injured in the Callanbridge Park area.
“Officers attended and found a 37 year old man with facial and other injuries.
“It was reported that the man had been attacked in a house in Callanbridge Park by three unknown males.
“The victim sustained fractures to his jaw and skull and required medical treatment.
“We would like to hear from anyone who has information in relation to this assault. We can be contacted at Ardmore Police Station on 101, quoting ref: 748070114.”
If you prefer to provide information without giving your details you can contact the independent Crimestoppers charity anonymously on 0800 555 111.