The number of people living with dementia worldwide is set to treble by 2050.
A new analysis by experts at the charity Alzheimer's Disease International says 44 million people live with the disease, but that figure will increase to 135 million by 2050.
The figures were released ahead of a G8 dementia summit in London next week.
The report says most governments are "woefully unprepared for the dementia epidemic".
Alzheimer's Disease International expects increasing life expectancies to drive a surge in cases in poor and middle-income countries, particularly in South East Asia and Africa.