A team of medics work in rotas to carry out duties for police forces including examining victims of crime and accused people who are held in custody.
Many are self-employed full-time GPs who use the part-time police work to top up their earnings.
Over the past three years the on-call doctor system has cost Scots police forces a total of more than £13 million.
Now, on the eve of the new national police service, politicians say savings must be made.
Scotland's largest force, Strathclyde, has paid £10,227,299 over the last three years to doctors, with the highest earning surgeon earning £261,156 in 2009/10, £207,333 in 2010/11 and £188,081 in 2011/12.
Nine of the doctors on its books were paid more than £100,000 last year.
Central Scotland Police paid £1,032,524 over the same period, with its highest earning doctor taking home £80,000 last year. Fife Constabulary's medical examiner earned more than £210,000 last year, while Grampian Police paid out £902,242 in the three years.
Politicians have criticised the sums and called for the medical profession and police chiefs to agree to reduce costs when the new single force comes into being in April.
Labour MSP Graeme Pearson, a former senior police officer, said: "The total cost for this service has reached unacceptable levels given the difficulties many patients face when it comes to accessing treatment outwith the custody environment.
"I expect the new national police service will, along with the medical profession, find a way to deal with these high costs."
Scottish Conservative health spokesman Jackson Carlaw MSP said: "It's essential Scotland's police officers are able to call on this kind of assistance.
"But many will see these astronomical figures and wonder what kind of value the public purse is getting.
"The fact anyone is getting up to £200,000 for effectively being on call is incredible, especially as so many of these individuals will have extremely well-paid regular jobs.
"With the creation of the single force little over a month away, it's vital this kind of spend is pushed down, without compromising the level of cover."
Other forces, including Lothian and Borders and Tayside, do not employ private doctors and use medical staff supplied by the NHS.
Payments for police surgeons are set by a national committee which includes senior officers, councillors and members of the British Medical Association (BMA).
Under the guidelines, police surgeons can be paid a retainer of up to £10,000 a year. Doctors can claim £80 for a first call-out between 7pm and 8am and each subsequent examination attracts a £52 fee.
Charges can also be made for issuing written reports and for business mileage.
Robert Oxley, campaign manager of the TaxPayers' Alliance said: "It's shocking that some police forces are spending millions of pounds of taxpayers' money on private doctors.
"Other constabularies manage to keep this bill down by using NHS doctors when they need medical staff, so clearly there are savings to be made."
A Strathclyde Police spokesman said: "Police surgeons are not employees of Strathclyde Police. Police surgeons provide a service outwith the NHS.
"The fees paid by Strathclyde Police for examinations, availability, travel, qualifications and so on, are based on the remuneration structure agreed by the Joint Negotiating Committee for Forensic Medical Examiners (JNC)."