"Austin Hospital, in Australia's second most populous city of Melbourne, erroneously killed off the patients when it faxed death notices to their family doctors.
The notices were the result of an inadvertent change to the templates the hospital sends to doctors once a patient has been discharged, operator Austin Health said in a statement.
"We apologized unreservedly to affected clinics who, for the most part, were very understanding about the error," it said.
Patient care had not been affected, the company stressed.
The Australian Medical Association said the error was unacceptable and potentially distressing to family doctors, while an opposition lawmaker said it was symptomatic of an overworked health system."