One mother was not told that her baby was seriously ill
Ombudsman Michael Buckley said complaints, which have increased year-on-year, have more than trebled since 1990.
He blamed three main areas for the rising complaints - ineffective communication, inappropriate treatment and a lack of support.
But he stressed he would only accept a lack of resources as an excuse if the staff had done their best for the patient.
Complaint numbers
"The fact that resources are limited does not automatically exonerate the body concerned from responsibility for poor service or treatment.
"It is not enough to say that the ward or clinic was exceptionally busy, if no steps had been taken to manage care appropriately in admittedly difficult circumstances."
This year Mr Buckley's office received 2,595 complaints and investigated 241 of them.
Sixty-nine per cent of grievances were upheld and 77% of all the cases investigated concerned matters of clinical judgement.
Mr Buckley said: "These figures show that my office is investigating a significantly higher proportion of complaints than in the recent past."
One of the cases highlighted included that of a mother who was not told her baby was critically ill until just before he died.
Mr Buckley criticised doctors at the Dudley Group of Hospitals in the West Midlands for their lack of communication.
He said the mother, who has not been named, was oblivious to the serious condition of her premature baby, who died a week after being put on a ventilator.
Mr Buckley said: "The lack of communication left the parents unprepared for their son's sudden decline and death."
Demenita case
In a separate case, staff at North Lakeland NHS Trust, in Cumbria were criticised over their handling of a dementia case.
A daughter complained that a consultant in old age psychiatry had told her that her father was not suffering from Alzheimer's disease.
She understood this to mean he was not suffering from dementia and agreed that he could be discharged into accommodation, which later proved to be unsuitable for him.
Mr Buckley said this was another example of staff not communicating adequately.
There were also complaints about essential nursing care.
These included the need for attention to bladder and bowel care, and the nutrition and hydration of older patients, especially those who were unable to care for, or speak for, themselves.
One case involved the daughter of a man suffering from dementia.
She said her father's condition had deteriorated markedly after he was admitted to Tees and North East Yorks NHS Trust.
It later emerged that he had been given inappropriate medication and there had been a failure to ensure he took enough fluids.
GPs were again criticised for the way some of them remove patients from their lists.
Mr Buckley said while most GPs accepted guidance from their professional bodies on when to remove patients he said that some patients still feared raising legitimate concerns because there GP might retaliate by striking them off his list.