More than 5,000 people died while on a health service waiting list in Northern Ireland last year.
The number of people passing away before being treated by hospitals has grown by a third since 2018, figures show.
In some cases, they had been waiting five years or more for treatment.
Health officials said the deaths may not be linked to being on a waiting list. However, the figures show how thousands of people are dying every year, often in pain and discomfort, before they could be seen.
Colm Gildernew MLA, who chairs the Stormont health committee, said: "Patients shouldn't have to spend their last months of life on a waiting list for treatments. It is an unthinkable burden to patients and their families, who are forced to watch precious time slip away."
According to the latest figures, more than 320,000 patients were waiting for their first consultant-led outpatient appointment as of December. More than 105,000 were waiting for inpatient or day-case treatment and around 145,000 were waiting for a diagnostic test.
The situation is expected to worsen because of a backlog created by the Covid-19 emergency.
Mr Swann warned MLAs yesterday it could take up to 10 years to return waiting times to an "acceptable level", with officials estimating the cost at £1bn.
Now data obtained by this newspaper, under Freedom of Information legalisation, reveals the human cost of the crisis.
It shows that:
• In the three years up to the end of 2020, a total of 13,269 patients died while on a waiting list in Northern Ireland.
• The number of people dying continues to grow year on year, from 3,854 in 2018 to 5,127 in 2020 - a rise of 33%.
• In at least 37 cases in 2020, the patient had been on a waiting list for more than five years.
• In 342 cases in the same year, the patient had been waiting for at least three years.
• The Northern Trust had the highest number of deaths on a waiting list last year (1,537), followed by the South Eastern Trust (1,045).
Writing in today's Belfast Telegraph, Health Minister Robin Swann says Northern Ireland has hospital waiting lists "that no civilised society should tolerate".
He states: "Far too many older people are spending their final years in pain and discomfort, hoping against hope that dates for surgery will be confirmed. We have to fix this."
Mr Swann also warns that significant and long-term recurrent funding will be needed to tackle the waiting list crisis.
Northern Ireland's health trusts recently issued a stark public warning about the health budget - pointing out that only £52.1m of the additional £495.2m allocated to the health service this year is recurrent, meaning the rest is not guaranteed for next year, thus causing problems around planning and investment.
Mr Gildernew added: "Chronic waiting lists in the north of Ireland have been an ongoing issue and to tackle them meaningfully will take significant investment and a robust strategy from the Department of Health."
Dr Paul Kerr, vice president of the Royal College of Emergency Medicine Northern Ireland, said: "As we exit the pandemic, there is no doubt that a top priority will be tackling the backlog of elective care. We know these waiting lists have grown very significantly over the past few years and we know that many people may be in serious discomfort and verging on a life-threatening condition."