Police are appealing for anyone who attended a New Years Eve party at 2 Herkomer Road, West Shore, Llandudno to contact them urgently.
Police were called to an incident at the address shortly after 5am on January 1 following reports of a disturbance which resulted in a man sustaining severe head and hand injuries.
Investigating officer PC Kate Bithell of Llandudno police station said: "This was a serious assault which has left the victim with extensive injuries and unable to work in the short term.
â€œWe believe there were more than 60 people at the party and we are keen to trace anyone who can assist in any way."
Anyone with information should contact PC Bithell at Llandudno police station on 101, if in Wales, or 08456071001 (Welsh line) 08456071002 (English line). Alternatively call Crimestoppers Cymru/wales anonymously on 0800 555 111 or text 66767 or email firstname.lastname@example.org