A 79-year-old man has been arrested for attempted murder following an incident at his home last night.
The victim, a 70-year-old woman who is known to him, is being treated at the Royal Sussex County Hospital, Brighton, where her condition is described as critical.
Police and ambulance were called to a house in Grasmere Avenue, Sompting, on Thursday at 6.45pm where a woman , aged 70, was found to have sustained serious head injuries.
DCI Mike Ashcroft, Surrey & Sussex Major Crime Team, said: "This is a tragic incident. We are conducting house to house enquiries and appeal to anyone with information of what happened to come forward.
"Forensic examinations are taking place and the man is helping police with our enquiries."
Anyone with information should contact police on 101, email email@example.com or call the independent charity Crimestoppers on 0800 555 111, quoting Operation Albany.