At about 3am today, emergency services were called to a unit complex on the Old Princes Highway, Engadine.
A 36-year-old man was found unresponsive.
A 33-year-old woman was arrested and taken to hospital for mandatory testing.
After she was released from hospital, the woman was taken to Sutherland Police Station.
She is assisting police with their inquiries.
Police continue to examine the crime scene in Engadine.
Anybody with information is urged to contact Crime Stoppers on 1800 333 000.
