People with a learning disability in Northern Ireland receive a poorer standard of health care doctors and nurses believe.
The Mencap survey found almost half of doctors and a third of nurses from a poll of 1,084 think this is the case.
The report found that some patients were treated with neglect.
The charity is urging health trusts to sign a charter which sets out rights of people with learning disabilities and the responsibilities of hospitals
The aim of Mencap's "Getting it Right" campaign is to ensure that no one with a learning disability should die as a result of ignorance and discrimination.
In 2007 the charity revealed that six patients had died unnecessarily in hospital.
Since then they have been developing a charter which they now want local health trusts to sign up to.
Mencap director, Maureen Piggott said there are nine specific actions that will make a difference.
"Training staff so they understand how to communicate with people with a learning disability, talking to the family and or other carers and even more fundamentally talking to the person themselves."
By law, all health care professionals must ensure people with a learning disability have access to equal health care.
But Mencap's survey found that almost half of health care professionals have not been trained in how to make reasonable adjustments for patients which, according to the charity, can often mean the difference between life and death.