More than 43,500 people travelled south of the Border to be seen as inpatient, outpatient or emergency cases in 2011, the latest year for which figures are available. The figure is a more than 12% up since 2008.
In one case highlighted by The Herald in 2010, patients in Ayrshire were being sent 200 miles to Middlesbrough for treatment because there was no specialist surgeon to treat them locally.
The issue has been the subject of a row between Labour and the SNP.
Labour insists the co-operation shows the value of remaining part of the United Kingdom. But the SNP has accused the party of scaremongering and pointed to a number of reciprocal health agreements between different states.
Tom Greatrex, Labour MP for Rutherglen and Hamilton West, said: "These figures indicate the substantial and increasing dependency of the NHS in Scotland on specialist services provided through the NHS in England.
"Even since 2008, the number of Scottish patients using the NHS in England has increased 12%, up from 38,835 in 2008 to 43,573 last year.
"While the administration of the NHS is devolved to Holyrood, the ability to make use of clinical expertise in specialist areas within the rest of the UK is becoming increasingly important.
"At present, that is part of how the NHS - a UK nationwide institution - operates."
Appointments at hospitals south of the border have increased year-on-year since 2007, according to statistics released by the UK Government.
Scottish patients can be treated at hospitals in England for a wide range of reasons, including for specialist treatments such as types of organ transplants.
Patients can also be counted while they are living in England temporarily, including for work or study.
It is also possible to opt to travel south of the border for treatment.
After the Middlesbrough case emerged the Scottish Government launched a review into the issue across Scotland, following reports that a number of other health boards were experiencing similar difficulties.
Mr Greatrex said the latest figures underlined the case of the Union.
He said: "Where centres of excellence exist, they are available and used by patients across the whole of the UK - and with a 12% increase in four years, that is increasingly the case for Scots relying on English NHS services.
"Using health services across borders, were Scotland to leave the UK, would mean doing so in a foreign country.
"Inevitably, this would be less straightforward than the situation now - where local services are determined locally, but the national service works across all of the UK in the best interests of the patient wherever they come from."
A Scottish Government spokesman said: "As was outlined in (the White Paper) 'Scotland's Future', the NHS in Scotland already co-operates with England, as well as with other countries for some services, to provide a range of specialised services not routinely available in Scotland.
"Access to a range of highly specialised services in England is managed and paid for by NHS National Services Scotland. These contractual arrangements would continue in an Independent Scotland.
"Similarly, services currently offered in Scotland to patients from England will continue in an Independent Scotland.
"The Westminster and Scottish Governments also have arrangements in place with a number of other nations, including the Republic of Ireland, for reciprocal treatment."