The 61-year-old doctor, who has not been named, has been questioned over the death of a grandfather who was taken to Darlington Memorial Hospital.
Alan Dunn, 60, from Ferryhill, County Durham, who had apparently stabbed himself, died after the knife was removed from his chest in December.
Durham Police said the surgeon had been questioned and bailed until April.
A force spokesman said a number of statements had been taken from staff at the hospital, but inquiries had not yet been completed.
Not suspended
A spokesman for the County Durham and Darlington Acute Hospital NHS Trust, which employs the surgeon, said: "We are co-operating fully with the police investigation and cannot comment further at this stage.
"We would like to express our sincere condolences to Alan's family."
The surgeon has not been suspended by the health trust but has voluntarily withdrawn from doing emergency work at the hospital.
He had earlier voluntarily attended a police station with his solicitor in December when he was arrested.
An inquest into Mr Dunn's death was opened and adjourned in January.
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