Alzheimer's Society in Wales: too many people waiting for diagnosis
Alzheimer's Society in Wales claim the number of people left without support after being diagnosed is "disgraceful".
The charity said the Welsh government has shown a commitment to improving things, but support varies widely across the country.
Local health boards are responsible for providing support for patients.
The charity is calling for a guarantee that everyone diagnosed with dementia will be assigned a named advisor to help them live with the condition.
The society said of the 45,500 people in Wales living with dementia, only 39% have a formal diagnosis, meaning there could be another 27,868 undiagnosed people living with the condition.
Ivor Williams, from Ystradgynlais, was diagnosed with Alzheimer's four years ago.
His wife, Wendy McCarthy Williams, said: "It took about 18 months to get a diagnosis. There was nobody to talk to, nobody to discuss it with.
"We had next to no advice or support. It was frightening to feel so alone. I had to do most of my research online and then happened to pick up an Alzheimer's Society leaflet at the hospital. Having someone to guide and support us made it all a bit easier to understand and cope with."
Sue Phelps, director of Alzheimer's Society in Wales, said: "Many people in Wales face daily challenges whilst living with dementia. It's disgraceful to think nearly two thirds of them have an added fight, to get a diagnosis. Everyone with dementia has a right to know."
The charity has launched its 'Right to Know' campaign to ensure people with dementia get diagnosed and access to information, support and available treatments.
It also wants a 66% dementia diagnosis rate across all areas with a commitment to reach 75% by 2017, a maximum waiting time of 12 weeks from people seeing their GP to diagnosis and a guarantee that everyone has access to a dementia adviser or equivalent after being diagnosed.
The Welsh government said it has invested £130m in new elderly mental health facilities Wales, including £58m for Llandough Hospital's EMI unit.
"We are improving the information and support available to people who suffer with dementia and their carers and training staff who provide care," said a Welsh Government spokesman. "This includes funding the Alzheimer's Society to provide special patient information packs, a free 24-hour Wales Dementia Helpline and books about dementia in every public library."