Governments around the globe are "woefully unprepared" to cope with the rising costs of dementia, according to experts.
The condition will cost some £388 billion globally this year – over 1% of GDP – including the cost of social care, medical bills and unpaid care by family members, researchers wrote in their World Alzheimer Report 2010.
But this figure will quickly increase in the future, with the number of people with the condition expected to double by 2030 and more than triple by 2050.
Experts at the Karolinska Institute in Sweden and King's College London examined the cost of dementia care and found that, if it was a country, it would be the world's 18th biggest economy.
And if it was a company, it would be the world's biggest by annual revenue, way above Wal-Mart (US$414 billion or £265.6 billion) and Exxon Mobil (US$311 billion or £200 billion).
The report was issued to coincide with World Alzheimer's Day and was commissioned by Alzheimer's Disease International (ADI).
Dr Daisy Acosta, chair of ADI, said: "This is a wake-up call that Alzheimer's disease and other dementias are the single most significant health and social crisis of the 21st century.
"World governments are woefully unprepared for the social and economic disruptions this disease will cause."
Professor Martin Prince, from the institute of psychiatry at King's College London, co-authored the report.
He said: "The care of people with dementia is not just a health issue – it is a massive social issue.
"This is particularly true in low- and middle-income countries which lack adequate systems of formal care.
"Governments must show greater leadership, working with all stakeholders, to drive solutions to the long-term care issue."