The Alzheimer's Society said it had found "shocking" evidence of poor and variable care during its review.
The report, based on Freedom of Information (FOI) requests, found problems with falls, night-time discharges and readmissions, and said standards needed to improve urgently.
The Department of Health said the disease was a key priority.
One in four hospital beds is believed to be occupied by a person with dementia.
The Alzheimer's Society called for all hospitals to publish an annual statement of dementia care, to include information on satisfaction, falls, readmissions and staff training.
The charity received responses to their FOI request from half of the 163 hospital trusts in England; however, for some of the questions the figures were based on a fifth of trusts as not all hospitals could provide answers to all the questions.
The information showed:
The Alzheimer's Society also carried out a survey of dementia patients. It found examples of patients being treated with excessive force, not being given enough help with meals and drinks and being left in wet or soiled sheets.
Nine in 10 said hospitals were frightening and only 2% felt all staff understood the needs of people with dementia.
The charity described these findings as unacceptable and a sign that dementia patients were not getting the standard of care they should.
Alzheimer's Society chief executive Jeremy Hughes said: "In the worst cases, hospital care for people with dementia is like Russian roulette. People with dementia and their carers have no way of knowing what's going to happen to them when they are admitted.
"In many cases they are well looked after but, as our investigation shows, too often people with dementia fall and injure themselves, get discharged at night or are marooned in hospital despite their medical treatment having finished."
A Department of Health spokesman said the disease was a key priority and in recent years Â£50m had been spent on making hospitals and care homes more "dementia friendly", while 500,000 staff had received extra training.
"People with dementia and their carers deserve the very best support," he added.
Dementia patients admitted to hospital in England play "Russian roulette" with their health, a charity is warning.