This year's World Alzheimer's Report focuses on caring for patients in the early stage of the disease, and identifying those who can benefit from treatments that are effective at that stage.
In some countries, as many as 90 percent of people with dementia might not be diagnosed, according to the annual report published by Alzheimer's Disease International, the federation of national Alzheimer's societies.
Worldwide, an estimated three out of four people with dementia have not been diagnosed, even though they might benefit from treatment.
Dementia - including its most common form, Alzheimer's disease - often starts with very subtle symptoms that even family members might not notice.
The report's lead author, Martin Prince, says there are ways to identify dementia patients that can be used, even in resource-poor settings.
"These are people who can be routinely diagnosed, using paper-and-pen tests - very simple clinical procedures that ought to be within the abilities and competencies of family physicians, you know, with some backup from specialist services."
Prince, with the Institute of Psychiatry at King's College London, says that early diagnosis can save money. Beginning a program of care early can delay very expensive institutional care later, at least in higher-income countries.
Experts reviewing thousands of scientific studies for the World Alzheimer's Report found that even in poorer countries, early treatment can delay the advance of symptoms and improve the quality life for patients and caregivers.
"It isn't very expensive care and I think particularly in low-income countries, where there's a lot of human resource, potentially," he says. "You know, spending some time with patients and their families is the sort of thing that realistically can be provided in a cost-effective way."
But to benefit from that, Prince says, people need to recognize that dementia, whose early stages often are marked by memory lapses, is not a normal part of aging.
"You know, your father's forgetful. So what, it happens all the time. That's how people are. And if you think it's a normal part of aging, then you're unlikely to go and seek help for it."