In three years up to the end of March this year, visitors who are not entitled to free NHS treatment received care worth almost £1.1 million at NHS Lothian facilities.
Of that amount, almost £300,000 has not yet been received by the health board, putting added strain on its already stretched finances.
Jackson Carlaw, health spokesman and deputy leader of the Scottish Conservatives, said more should be done to recoup the sums.
He said: “Of course if someone is visiting the Lothians and requires emergency medical attention we can’t stop them at the door to demand cash. But it should not be beyond the wit of our health service to ascertain one’s ability to pay before receiving elective treatment.
“NHS budgets are under pressure. That makes it even more crucial that the people of Edinburgh aren’t losing out because of those who are not entitled to free care taking thousands out of the system.”
Mr Carlaw said many of the procedures carried out had been pre-planned, rather than emergencies, and that it could be “nigh-on impossible” to get payments after the foreigners left the country.
The £292,712 owed to NHS Lothian accounted for nearly 30 per cent of the £912,813 Scottish total owed.
Many of the NHS Lothian departments which carried out procedures on foreigners, such as general surgery, urology and plastic surgery, are struggling to treat patients who live in the Edinburgh area on time.
Americans were by far the most frequent non-NHS users of NHS Lothian between April 2009 and March, clocking up bills totalling £462,000.
Canadians were billed £53,895 over the three years.
People from Barbados, Fiji, Tibet, Bermuda, the UAE and Trinidad have also made use of NHS Lothian facilities despite not qualifying for free treatment in Scotland.
Cardiology departments provided the most expensive treatment to foreign nationals, sending out bills of almost £190,000 in total.
Some of the outstanding cash may be owed by patients who had insurance but are in a dispute over what was covered.
A spokeswoman for the Scottish Government said measures were in place to make sure overseas patients paid for treatment. She added: “Where necessary, NHS boards should discuss procedures for pursuing debt with the Central Legal Office, which has a contract with an international debt recovery company.
“Boards must also pass full details of non-payers to NHS Scotland Counter Fraud Services who will liaise with the UK Border Agency.
“Non-payers can then be refused re-entry to the UK until they settle their bill.”