Elderly people suffering from memory loss need to act more quickly in seeking medical advice, says The Alzheimer's Society.
According to the charity, up to two-thirds of people in England with dementia are never diagnosed as they do not recognise the symptoms.
It is estimated that by 2025 more than 1 million people in the country will have dementia. The Department of Health is backing the Alzheimer's Society campaign to raise public awareness of symptoms and the importance of an early diagnosis.
Health Minister Ivan Lewis said: "Dementia is now one of the most significant health challenges facing our society. That is why we are determined to bring dementia out of the shadows."
Currently 700,000 people in the UK live with the disease and one-in-three people over the age of 65 will die with it.
For those who do report their symptoms to the GP, it takes an average of nearly three years for a diagnosis from first noticing symptoms, the Alzheimer's Society said.
Neil Hunt, its chief executive, said: "There is an acute lack of awareness and understanding of dementia. By encouraging people who are worried about their memory problems to seek medical advice sooner than they might have done, we hope more people with dementia can get care early on, giving them a greater chance to live life as well and as fully as possible."
The Alzheimer's Society is giving GPs in England posters and leaflets to raise awareness about the issue and a toolkit to support diagnosis.