The NDIS will not be able to cope effectively with younger people with dementia, says Alzheimer's Australia.

One in 13 Australians with dementia is aged under 65, say campaigners concerned about their plight under the national disability insurance scheme.

Alzheimer's Australia estimates that at least 25,100 younger people have dementia, including some in their 30s and 40s, and expects the figure will jump to 36,800 by 2050.

"The number of people with Younger Onset Dementia is underestimated because of the lack of recognition in diagnosis and misdiagnosis," says the organisation's CEO Carol Bennett.

Launching the No Longer A Statistic campaign on Thursday, Ms Bennett said the organisation was concerned about the future of its pioneering federally-funded Key Worker program.

Since 2013, thousands of people have been helped through its specialised one-on-one support.

But the organisation fears the service will be rolled into the NDIS, which it says won't be able to cope effectively with younger people with dementia.

Ms Bennett said the NDIS model deals directly with the individual but the Key Worker program incorporated the person's family and carers.

People needed a diagnosis to access the NDIS but that often takes years with dementia.

"Our program works with families at the point they are having problems and noticing symptoms, giving them support and the services they need," Ms Bennett said.

She said the organisation wanted to reach a compromise with the government to ensure the needs of the younger people were met, whether this was in conjunction with the NDIS or separately.