Some patients were not offered help with eating or bathing, and one was left in urine-soaked clothes held together with paper clips.
Older people too often did not receive the care, compassion and respect they deserved, according to the ombudsman, Ann Abraham.
Her report cites 10 cases inadequately investigated by the NHS, in which elderly men and women were treated appallingly, often towards the end of their lives. It details serious failings in how NHS staff managed the patients' pain, nutritional needs and discharge from hospital, often with disastrous consequences.
Her disclosures led to calls for the NHS to urgently overhaul its care of the elderly.
"These often harrowing accounts should cause every member of NHS staff who reads this report to pause and ask themselves if any of their patients could suffer in the same way. I know from my caseload that in many cases the answer must be 'yes'," said Abraham.
The 10 anonymous cases outlined in the report include:
• Alzheimer's sufferer Mrs J, 82, whose husband was denied the chance to be with her when she died at Ealing hospital in west London because he had been "forgotten" in a waiting room.
• Mrs R, a dementia patient, who was not given a bath or shower during 13 weeks at Southampton University Hospitals NHS trust. She was not helped to eat, despite being unable to feed herself, and suffered nine falls, only one of which was recorded in her notes.
• "Feisty and independent" Mrs H, who had lived alone until she was 88, was taken from Heartlands hospital in Birmingham to a care home in Tyneside but, when she arrived, was bruised, soaked in urine, dishevelled, and wearing someone else's clothes, which were held up with large paper clips.
• Mr C suffered a heart attack soon after undergoing quadruple coronary artery bypass surgery at Oxford Radcliffe Hospitals NHS trust. Trust staff turned off his life support machine even though his family had asked for them to wait for a short while longer.
The care services minister, Paul Burstow, said that the report underlined the urgent need to modernise the NHS. "The dignity of frail older people should never be sidelined," he said.
Leadership by frontline NHS staff was needed to drive out poor practice, he added. An initiative by the Care Quality Commission NHS regulator in England would start next month, Burstow added. This will see spot inspections by nurses to check up on malnutrition and dignity among older patients.
Elderly patients represent more than 75% of those cared for by the NHS, and 60% of those who stay in hospital. The ageing population means they form a growing proportion of the service's workload.
"The inhumane treatment of older people described in this report is sickening and should send shockwaves through the NHS and government. It's difficult to imagine us allowing any other group of people to suffer this indignity and neglect," said Michelle Mitchell of Age UK.
The Patients Association said the ombudsman's report was "damning". Chief executive Katherine Murphy said: "It is a sick joke that we have an NHS constitution that tells us what rights we have when being treated by the NHS, but it is clear that, to the majority of older patients, it is not worth the paper it is written on."
The association wants independent matrons on wards to check that every patient is being cared for properly, added Murphy, an ex-nurse.
Peter Carter, chief executive of the Royal College of Nursing, said the report should act as a wake-up call to NHS personnel and regulators. But he warned that staff reductions and the £20bn savings drive would affect frontline care.
"Where we have seen poor standards of care in the past, we have often found an underlying failure in ensuring safe staffing levels and the right level of skill. Just last week 80% of RCN members surveyed told us that they did not have enough staff to deliver good quality care to patients," said Carter.
The report's findings have been made public as Liberal Democrat leaders try to stifle a revolt over the coalition's NHS reforms. Party critics claim the reforms will increase health inequalities, make tracts of the NHS unviable, and simply provide profits for private firms asked to take on the task of commissioning care. New figures show the reforms will cost £1.8bn to implement.
The Department of Health yesterday revealed it had sought authorisation from parliament to set the money aside to cover redundancy payments, pension liabilities, and the penalties of breaking contractual obligations of the primary trusts.
But the political backlash poses the greatest risk for the coalition, as Lib Dem rebels attempt to raise it at their spring conference next month.
Privately many cabinet members have doubts about the politics of health reforms, if not the reforms themselves, and rejection of them by one wing of the coalition would increase those doubts.
Failings and missed opportunities
The other six cases outlined in the report:
Advanced stomach cancer patient. Family found him in a "distressed" condition behind drawn curtains on day of discharge from Royal Bolton Hospital NHS Foundation Trust. Discharged with inadequate pain relief, leaving family to find someone to dispense morphine over a bank holiday.
Died from peritonitis and a perforated stomach ulcer after GP surgery missed opportunities to diagnose an ulcer. Ombudsman upheld complaints about the Epsom and St Helier University Hospitals NHS Trust and the GP surgery.
Suffered from depression and dementia, 79. Admitted to St Peter's Hospital, part of Ashford and St Peter's Hospitals NHS Foundation Trust. His life was put at risk when the trust stopped treating him and then discharged him when he was not medically fit.
Aged 84. Doctors at her local surgery failed to review her medication after she left hospital, with "serious" consequences for her health.
Parkinson's disease sufferer, 72, a "brilliant" architect who enjoyed keeping fit. Care and treatment by Surrey and Borders Partnership NHS Foundation Trust contributed to a "loss of his dignity" and "compromised his ability" to survive pneumonia.
Lung cancer patient. Doctors at Northern Lincolnshire and Goole Hospitals NHS Foundation Trust neglected to address the severe pain she was suffering.
I'm not the least bit surprised by this. Horrified, certainly, but not surprised. This report is long overdue.
Mods, could we have an NHS tag please?