Three-quarters of doctors say sufferers are forced to rely on family, friends, neighbours and other unpaid carers.
And many doctors admit that they do not feel they have had enough training to deal with people with dementia.
The poll by charity the Alzheimers Society found that half think the NHS is doing too little for sufferers.
More than two-thirds believe patients do not get enough help from adult social services after diagnosis.
Jeremy Hughes, chief executive of the Alzheimers Society, said: Our survey gives a stark view from the doctors surgery of people with dementia left struggling in the aftermath of a diagnosis.
GPs report a deeply worrying lack of support from health and social services, with relatives left to pick up the pieces alone. People can need a lot of help to live well with dementia.
Families and friends are a vital source of support but they mustnt be relied on to do everything.
The charity said the poll of 1,000 GPs shows that hundreds of thousands are being let down and ministers must ensure that everyone with dementia gets a full package of support, including a dementia adviser with better help for those caring for relatives.
Carer Stephen Blakeburn, 50, from Darlington, whose mother Jenny, 86, suffers from dementia, said: We feel like weve been failed by a system which doesnt work for us.
A Department of Health spokesman said training had been given to 600,000 NHS and social care staff, adding: Our diagnosis rates are now among the highest in the world.
Source The Sunday Express
