Police are investigating an attempted murder at a flat in Polegate.
Police said the victim, a 47-year-old woman, was found with serious injuries at an address in Brookside Avenue before 10pm on Wednesday (October 22).
She had been stabbed, police said.
She was taken to the Royal Sussex County Hospital, Brighton, where she is being treated.
Her condition is described as critical, police said.
Detective Chief Inspector Mike Ashcroft, of the Surrey and Sussex Major Crime Team, said: “This is being treated as a domestic incident.
“We are not seeking anyone else in connection with this investigation and we would like to reassure other residents that there is nothing to cause them concern.”
A 73-year-old Polegate man has been arrested on suspicion of attempted murder and is currently in custody helping police with their enquiries, police said.