A fifth of patients with a disability were unsatisfied with their care at Hampshire Hospitals Trust, new figures show.
Disability Rights UK said the low satisfaction figures across England should give NHS providers a "wake-up call to do better" when it comes to caring for patients with a disability.
The patient-led assessment of the care environment is an annual survey of NHS patients, who review the care they received across a variety of topics, including privacy, food, and cleanliness.
It shows 81.7% of patients with a disability who received care at Hampshire Hospitals NHS Foundation Trust last year were happy with their treatment – below the average of all providers across the country at 82.5%.
Fazilet Hadi, head of policy at Disability Rights UK, said the low satisfaction rates nationally "should give NHS and independent care providers a wake-up call to do better".
"It is not good enough that one in five people with dementia or a disability are not satisfied with the care they receive," Ms Hadi added.
She also explained that people's expectations of care are lower than they should be, meaning the true gap between the quality of care that should be provided and what is actually offered is even larger than these figures indicate.
Meanwhile, the figures show 80.6% of dementia patients across the country were satisfied with the level of care they received – this rose to 81.5% at Hampshire Hospitals Trust.
The survey also showed Hampshire Hospitals NHS Foundation Trust scored 99.5% in its levels of cleanliness, 92.3% in the food and drink served, and 80% in the dignity and wellbeing of the patients.
The trust also scored 90.5% in condition, appearance, and maintenance.
A Department of Health and Social Care said it is supporting social care with up to £7.5 billion over the next two years, and will soon publish a Major Conditions Strategy, covering six conditions, including dementia, to set out the standards patients should expect.
A spokesperson said health and care staff will also receive learning disability and autism training.
They added: "We want a society where every person with dementia or a disability, along with their families and carers, receive high quality, compassionate care – and it’s great to see that over 80% of people are happy with the care they receive."