One woman in her late 90s died in her granddaughter's arms after she was discharged from hospital without being properly examined.
Many patients are being discharged from hospital before they are medically fit to leave or ready to cope at home, according to a new report from an NHS watchdog.
Some are being sent home "alone and afraid", while relatives and carers are not always being told when patients are discharged.
The report by the Parliamentary and Health Service Ombudsman (PHSO) cited "harrowing" examples of people being "badly let down by the system".
In one case, a woman in her late 90s died in her granddaughter's arms moments after being dropped off at home after she was discharged without being properly examined.
The PHSO also found a father's death from sepsis could have been avoided if he had been treated for the condition before he was discharged.
In another case, an 85-year-old woman with dementia was sent home alone at 11pm without her family being informed.
"Our investigations have found that some of the most vulnerable patients, including frail and older people, are enduring harrowing ordeals when they leave hospital," said the PHSO's Julie Mellor.
"Poor planning, co-ordination and communication between hospital staff and between health and social care services are failing patients, compromising their safety and dignity.
"Health and social care leaders must work harder to uncover why ten years of guidance to prevent unsafe discharge is not being followed, causing misery and distress for patients, families and carers."
Caroline Abrahams, charity director at Age UK, said the "dreadful cases" marked "a new low in what looks like a continuous downward trend in the capacity of our health and care system to look after our older people adequately - indeed, on occasion even in its ability to keep the most vulnerable safe and alive".
NHS Improvement said better discharge processes were being worked on to ensure vulnerable patients are protected.
A spokesman said: "Rather than frail elderly people staying in hospital longer than they need to, it is better to get patients home as quickly as possible and to assess them in their own homes rather than in a hospital - but this must be done with the right help and support in place."