Two-thirds of people over the age of 50 fear that they will develop the condition while just one in 10 said they were frightened about getting cancer.
When 500 adults aged over 50 from across the UK were asked which condition they feared the most, 68 per cent said dementia and 9.44 per cent said cancer.
Meanwhile just 3.88 per cent said they were frightened about getting a heart condition and 0.73 per cent were concerned about developing diabetes.
There are around 800,000 people with dementia in the UK but as the population ages this figure is expected to soar in coming years.
Symptoms can include memory loss and difficulties with thinking, problem-solving or language. It occurs when the brain is damaged by diseases, such as Alzheimer's disease or a series of strokes.
Paul Green, director of communications at over-50s company Saga, which conducted the survey, said: "Whilst these fears are completely understandable, it's important that education around the condition is enhanced to give a greater understanding of the benefits of early diagnosis - and how this can help those living with the condition continue to lead fulfilling lives."
Commenting on the poll Hilary Evans, director of external affairs at charity Alzheimer's Research UK, said: it was no surprise to learn that fear of dementia in people over 50 is high. "The challenge is to find new ways to treat and prevent dementia to show there is hope of taking on dementia and beating it."