Police spokesman Johann Baumschlager says that an inquiry into "quackery" is under way.
According to the daily newspaper Kronen Zeitung, the Viennese man had administered blood transfusions, attended acute cases and was even a race doctor at official motorcycle events.
The actions of the 59-year-old remained undetected for years, mainly due to the involvement of his partner, a doctor at the Lower Austrian Provincial Health Directorate.
The woman had applied to perform emergency services on weekends, then when emergencies came up, she sent her partner.
"For us, this is very surprising," Deputy Director of the State Health Department, Robert Kellner, told the Austrian Press Agency.
The 'quack' had carried out his work for years "to the fullest satisfaction," said Kellner. "We never had any problems."
When the case became public, the doctor herself resigned, despite the work she performed with her partner being a secondary activity.
According to the Kronen Zeitung, all patients were satisfied, even after being treated by the fraudulent doctor, who had apparently also covered for his partner while she was on annual leave.