A 24-year-old man was seriously injured when he was stabbed outside a house on Mill Road, Dundalk, at around 10pm last night.
He was taken by ambulance to Our Lady of Lourdes Hospital, Drogheda.
A man, aged in his 20s, was arrested in connection with the incident and is being detained at Dundalk Garda Station.
The scene has been preserved for a technical examination.
Gardaí are appealing for witnesses.
Anyone with information is asked to contact Dundalk Garda Station on 042-9388400 or the Garda Confidential Line 1800-666111.