Too many older people are "suffering in silence" when things go wrong with their NHS care, the Parliamentary and Health Service Ombudsman (PHSO) has said.
Elderly people often rely on relatives to raise concerns when things go wrong with hospital care, the PHSO said, but a new poll found that some family members find it difficult to raise concerns.
In a new survey, relatives of elderly hospital patients raised a number of concerns over care including an older male patient having to dial 999 after a fall in his hospital room and a patient put in to an adult "nappy" instead of being given help to go to the toilet.
The NHS needs to make clear to patients that their care will not be compromised if they, or a relative, makes a complaint, the ombudsman said.
The PHSO and the website Gransnet surveyed 600 people who had an elderly family member who had stayed in hospital overnight in the past year.
The organisations found that more than one in three (35%) said there were occasions when they were concerned about the care or treatment of their older relative in hospital.
Of these, 58% said they felt compelled to complain.
Among those who had raised concerns, half said it was "difficult" to complain and only 37% said they felt their concern was listened to and taken seriously.
Only 27% said they felt their complaint made a difference.
Among those who said they were concerned about care but did not complain, 19% said they were worried about the impact that complaining would have on the care and treatment of their relative.
And a third said they did not complain because they did not think anything would change, while 6% said they did not know how.
Relatives also provided brief descriptions about their concerns over care. One wrote: "After a fall my husband had to call 998 (999) for help. In his hospital room! No-one came. Lay on the floor for 75 minutes in agony before a doctor could be found."
Another added: "If we didn't visit at meal times I don't think my father would have eaten as he wasn't able to feed himself but the staff didn't feed him either."
One wrote: "The staff use adult 'nappies' for patients who can't get out of bed. However, these were used as a convenience as when my dad was better and could get out of bed with help and asked to use the commode he was told to do it in the nappy as there was no-one available to help him. This happened on many occasions and made him really upset."
The PHSO said there are far fewer complaints from older people than would be expected given older people's high usage of NHS services.
A previous report from the PHSO highlighted that many older people are afraid to raise the alarm when something goes wrong in their care and worry about what will happen to them if they do.
"The NHS is a lifeline for many vulnerable older people but, when things go wrong, too many are suffering in silence," said PHSO Rob Behrens.
"I want people to be confident to complain, know their rights, and speak up when things go wrong so that the NHS can learn from mistakes and improve services for others.
"NHS staff should make patients and their loved ones aware of how to complain, point them to available support, and make it absolutely clear that their future care will not be compromised."
Lara Crisp, editor of Gransnet, said: "Patients deserve better than this. While we appreciate that services are stretched, communication with patients and their families must be improved. They should feel that their concerns are taken seriously and addressed properly.
"It's simply not acceptable that over half of people with a concern feel they can't complain or that it won't make any difference if they do.
"Hospital staff need to be supported and enabled to communicate better with patients so that everyone is clear about the complaints procedure and patients are reassured that this will not affect their future care."
A Department of Health spokeswoman said: "We are determined to make the NHS the safest healthcare system in the world, but when things do go wrong, it's incredibly important to listen to patients' and families' complaints or wider feedback.
"By learning from mistakes we can improve care. This is why we made complaints handling a crucial element of the hospital inspection regime.
"These findings show more could be done to help older people and families complain. We are clear that organisations should be open about how to complain and clearly communicate the support available to people who need help complaining."