Doctors and nurses are discriminating against people with learning disabilities, a charity said today.
A survey for Mencap found health professionals had witnessed discrimination by their colleagues, with patients suffering a lack of respect and dignity.
Overall 46% of doctors and 37% of nurses said they believed people with learning disabilities received poorer NHS care than other groups.
Almost half of doctors (45%) and a third of nurses (33%) personally witnessed a patient being neglected or suffering a lack of dignity on the NHS, or receiving poor quality care.
Some 39% of doctors and 34% of nurses, from the poll of 1,084, said they thought patients suffered discrimination.
Mencap's 2007 report, Death by Indifference, highlighted six cases of people with a learning disability who died unnecessarily in NHS hospitals.
Since then, the charity has received more "tragic accounts", it said.
All people with learning disabilities should receive equal treatment by law, with the NHS making "reasonable adjustments" where necessary.
But today's poll found 35% of doctors and nurses received no training in how to make reasonable adjustments, which Mencap said can "mean the difference between life and death" for patients.
Many health professionals said they needed specific guidelines on how care and treatment should be adjusted.
Mark Goldring, Mencap's chief executive, said: "Healthcare professionals have recognised they need more support to get it right when treating people with a learning disability.
"Mencap's Getting it right campaign sets out to ensure that ignorance and discrimination need never be the cause of death of someone with a learning disability."
In one case, Emma Kemp, 26, had a learning disability and was diagnosed with cancer.
Her mother Jane was told Emma had a 50% chance of survival with treatment, but the hospital staff were worried it would be difficult to treat her because of her learning disability.
Emma's doctors decided not to treat her, saying that she would not co-operate with treatment.
Her mother eventually agreed that palliative care would be appropriate.
She told Mencap: "Emma was a fun-loving young woman who loved her life and all of the people in it.
"She was denied her chance of life by doctors who discriminated against her. One doctor actually said: 'If she was a normal young woman we would not hesitate to treat her'.
"When I agreed that Emma should only receive palliative care treatment, I did so because I was then told that Emma only had a 10% chance of survival and that it would be cruel to treat her.
"I now know that this was not true, that I was misled into agreeing with the decision that cost my daughter her life."
Niall Dickson, chief executive of the General Medical Council, said: "We strongly support this campaign.
"Every patient is entitled to the care and treatment they need and the vast majority of doctors do everything they can to achieve this, making the care of each of their patients their first concern.
"But we also know from the evidence that professionals can struggle with the complexities involved in treating patients with learning disabilities, and under pressure they can make assumptions about the needs and wishes of these patients.
"Sometimes they see the disability, rather than the patient or their underlying condition."
Dr Peter Carter, general secretary of the Royal College of Nursing (RCN), said: "People with learning disabilities often experience poorer health and are twice as likely to be admitted to hospital.
"Their health needs can go unrecognised, which has an impact on both quality of life and life expectancy.
"Like all patients, people with learning disabilities should be fully supported and treated with dignity and respect."
A Department of Health spokesman said: "The NHS is for everyone and removing inequalities is a priority.
"Improvements have been made in delivering healthcare for people with learning disabilities but there is still much to do. Health remains one of the three priorities for the Government's learning disability strategy."