The number of people waiting more than a year for an operation in Wales has risen by more than 400% in the past four years.
A freedom of information request by the Royal College of Surgeons revealed the number of people waiting more than 12 months for surgery in the year ending March 2017 was 3,605.
In March 2013, the figure was 699.
The number of patients waiting more than a year for treatment in England - which has more than 17 times the population of Wales - was just 1,302.
Last month, the Labour-controlled Welsh government pledged £50 million to tackle the problem. It emphasised that the number of people waiting 26 weeks and 36 weeks for an operation has fallen.
But the Welsh Conservatives slammed the figures, claiming the Welsh NHS was "staring into an abyss".
Betsi Cadwaladr University Health Board (BCUHB) and Abertawe Bro Morgannwg University Health Board (ABMU) saw the greatest leap in patients waiting more than a year.
BCUHB had no patients waiting beyond a year in 2013, compared with 1202 in 2017.
The number of patients having to endure long waiting times at ABMU jumped from 49 to 1,271 over the same period.
Trauma and orthopaedic surgeries had the largest rise in long waiting times, with 2,489 patients waiting more than a year in 2017, compared with 39 in 2013.
Despite the increase in patients waiting more than a year, the number of people waiting more than 26 week and 36 weeks has fallen.
The number of people waiting more than 36 weeks from a GP referral to treatment was 12,354 in March 2017, down from 28,654 in August 2015, according to the Welsh Government.
Earlier this month, Welsh Health Secretary Vaughan Gething promised a further £50 million to cut waiting lists.
A Welsh government spokesman said: "Despite increased demand on the NHS in Wales, the health service is treating more patients, with the vast majority being seen within target times.
"Over the last five years, referrals to hospital-based services have increased by around 20% - from 1.07 million in 2012/13 to 1.27 million in 2015/16.
"Increases in individual specialities are even higher, with orthopaedic referrals alone up 22%.
"Despite this, latest figures show over half of patients are waiting less than 10 weeks for treatment, while there has been a 28% reduction in the number waiting over 36 weeks in March 2017 compared with the same period in 2016.
"However, we acknowledge some people are still wait too long for treatment. That's why we established the planned care programme to help NHS Wales deliver sustainable services.
"In addition, health boards have action plans in place to reduce long waits, and earlier this month, the Health Secretary announced an extra £50 million to help the NHS further improve waiting times."
But Angela Burns, Welsh Conservative Shadow Health Secretary said: "No one should have to wait more than a year for surgery, but that's becoming a painful reality for more and more NHS patients in Wales.
"That nearly three times as many patients in Wales - a country 17 times smaller than England - waited more than 52 weeks for surgery really underscores the hypocrisy of Jeremy Corbyn and his Labour party.
"He and his comrades have in the past flattered themselves with the moniker of 'a government in waiting', but here in Wales, Labour are little more than the government of waiting times, which continue to grow unabated.
"Betsi Cadwaladr health board, which went into special measures - the highest form of Welsh Government control - two years ago, has seen its year-plus waiting times go from zero to 1,202 in that time.
"The longer patients are allowed to languish on waiting lists, the more complex their needs become, and the more expensive their treatment is to minister.
"In the absence of a long-term strategy, the Welsh NHS is staring into an abyss. It's up to the Labour administration to finally get a handle on the situation or face a health service beyond repair."
Tim Havard, regional director for Wales at the Royal College of Surgeons, said that the problem could be tackled by a renewed focus on community care.
He said: "A patient's condition can also deteriorate the longer they are made to wait for treatment, meaning the eventual outcomes are not as good as they could have been.
"The Welsh health service is facing a raft of pressures, with hospital wards being filled with patients that should be treated in the community and a continued squeeze on finances.
"Improving the availability of community beds, primary care, and caring for people in their own home would significantly reduce unnecessary and prolonged hospital admissions.
"The ongoing parliamentary review of health and social care in Wales offers an opportunity to confront some of the problems causing long waits for treatments and give patients the timely access to care they require."
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