MELBOURNE'S growth corridors will be hardest hit by an expected surge in dementia cases, projections show.

A report by Access Economics for Alzheimer's Victoria, released today, shows that the cities of Casey, Brimbank, Yarra Ranges and Greater Dandenong will experience some of the largest increases in dementia cases over the next four decades.

These areas will bear the brunt due to their large concentration of people in their 20s, 30s and 40s.

The prevalence of dementia will also increase as baby boomers hit their twilight years. Without a breakthrough, the number of people with dementia in Victoria is expected to almost quadruple from about 66,000 people today to 246,000 by 2050.

Alzheimer's Victoria chief executive officer Lynette Moore said the modelling showed that governments needed to start funding services in areas of greatest need.

She said her organisation was sending the data to every state and federal MP in Victoria in an effort to ''sharpen their focus'' on increasing funding for dementia.

Ms Moore said there were waiting lists of three to six months to be assessed for dementia in Victoria under a state government program.