The future global burden of Alzheimer's and other types of dementia has been underestimated, say UK experts.
A report from King's College London suggests more than 115 million people across the globe will suffer from dementia by 2050.
This prediction is 10% more than previous figures published in 2005, driven mainly by new figures from South Asia and Latin America.
The Alzheimer's Society said the data showed the "scale of the challenge".
The rise in dementia fuelled by increasing life expectancies in countries around the world is causing widespread concerns.
The strain of caring for people with dementia is not just a social issue, but an economic one, placing a growing burden on the working population and health systems.
The King's College London research, part of the 2009 World Alzheimer's Report, published by Alzheimer's Disease International, estimates that there will be 35 million people worldwide with dementia by next year.
That number is set to almost double every 20 years, to 65.7 million in 2030 and 115.4 million in 2050.
Advances in healthcare and nutrition will have the biggest impact in poorer countries and, as a result, the number of older people is set to increase rapidly.
Currently, it is calculated that just over half of all people with dementia live in poor- or middle-income countries, but this is expected to rise to more than two-thirds by 2050.
In addition, the research suggests that the proportion of older people who have dementia is higher than previously thought in some parts of the world, adding to the estimated numbers.
Professor Martin Prince, from King's College, said that the numbers involved were "staggering".
He said: "The current investment in research, treatment and care is actually quite disproportionate to the overall impact of the disease on people with dementia, the carers, on health and social care systems, and on society."
Alzheimer's Disease International said that more countries should follow the lead of Australia, France, Korea and the UK in developing action plans to tackle the impact of the disease.
The Alzheimer's Disease Society said that the UK could still do more, with one million people set to develop the illness in the next decade.
A spokesman said: "This shows the scale of the challenge. This worldwide problem needs a response from every nation and the UK government must play a key part."