Massive variation in the amount paid by different health boards has been exposed by the data obtained using the Freedom of Information Act (FoI).
Health boards tend to send patients to private hospitals for procedures when they are struggling to treat them within official waiting times guarantees.
The bill for private-sector use came to light days after a Medical Practitioners Tribunal Service hearing found a surgeon who treated NHS patients at a private hospital in Glasgow failed to provide "good clinical care".
In a number of cases Colin Campbell Mainds, 56, who operated in BMI Ross Hall Hospital, was found to have placed spinal implants incorrectly.
In addition, he did not examine three patients adequately and did not provide two patients with enough information about the risks of the procedures they were facing.
Jackie Baillie, Scottish Labour's Shadow Health Secretary, who obtained the data on private-sector expenditure by the NHS, said: "To find out we have spent so much money sending patients to private hospitals is astonishing. It shows the NHS in Scotland simply doesn't have the capacity it needs to meet patient demand."
When the SNP established a minority government in Scotland in 2007, then health secretary Nicola Sturgeon ruled out investing more taxpayers' money in private surgery units and hospitals.
Andy Kerr, health secretary for the previous Labour administration, had spoken of a "longterm relationship between the NHS and the independent health sector" and pledged £45m over three years to negotiate contracts.
Ms Sturgeon said health boards could use existing private-sector capacity "at the margins" to reduce patient backlogs.
The new figures show a spend of £34.2m in 2011/12 and £36m in 2010/11.
NHS Fife spent less than £4000 in both years, while NHS Borders spent over £4m – more than NHS Greater Glasgow and Clyde at around £3.5m.
NHS Lanarkshire appeared to have the highest spend at £9.1m for both years, but this may be a reflection on how they answered the FoI question. The health board said more than 70% of the spend on independent health services went on care home and hospice services.
Professor Allyson Pollock, expert in public health research and policy at Queen Mary, University of London, said: "It is not sensible to use the private sector for pragmatic reasons, far better to ensure there is sufficient capacity in the NHS and to plan accordingly. The NHS can have flexibility built in to the system."
Health Secretary Alex Neil said: "Our health service is run for patients, not profits, which is why we choose to give the NHS real terms funding increases in the face of UK Government cuts.
"The number of patients treated in the private sector is a tiny fraction of the total – most patients are treated locally."
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