About 84% of people with mental health problems and a third of the UK general public feels isolated, according to a new report.
Many people in the UK feel cut-off from society
The charity Mind says young people are most likely to feel disconnected from society, whether they have mental health problems or not.
It blames lack of relationships, absence of support and discrimination for feelings of social exclusion.
The charity is calling for government action on the problem.
Surveys of 532 Mind members and 964 members of the general public showed people living in rural communities and from black and ethnic communities were also more susceptible to isolation.
People in East Anglia, Yorkshire and Humberside and the South East appeared to be the most isolated in the UK.
mental health problems
living in rural or minority areas
People living in the North seemed to be the best supported.
But 83% of the public said they had never felt isolated.
Younger people also reported higher rates of isolation - 92% of 18-24 year olds with mental health problems and 35% of adults aged 15-24 felt isolated.
Feelings of social exclusion were most common among people with mental health problems and often contributed to their illness.
Of the Mind members surveyed, 80% said isolation made it harder for them to recover or cope with their mental health problems.
Many blamed relationship problems or lack of close relationships stemming from their mental health problems, as a top cause of isolation.
Unemployment, lack of money and lack of support services also featured highly.
Ready use of a telephone was mentioned most often as the support used to help overcome isolation. But, one in 10 of those questioned said they did not have easy access to one.
Mind said many people with mental health problems were condemned to a life of social segregation because of a vicious cycle of isolation, worsened by stigma and prejudice.
Chief executive Richard Brook said: "Most people already know that it's good to talk, but when you're in mental distress it isn't always that simple. If the crucial links are missing things can go downhill rapidly."
He urged the government to take the lead in providing better social support for those at risk.
"There needs to be more relevant social care services in place and better understanding by us all to enable people in mental distress to get back on their feet and back into society," he said.
A spokeswoman for the Samaritans said there was still a huge amount of stigma attached to mental health problems, despite them being common, which makes it hard for people to discuss their problems.
"In general, there is a very stiff upper lip attitude in the UK, which can make it hard to seek help.
"Ultimately, we need a change in attitude so that mental health is on a par with physical health and is not a dirty word," she said.