Men were less likely to report feeling stressed
Young adults are suffering from "anxiety overload", a UK charity warns.
A survey of 18-24 year olds found 66% feel stressed or anxious at least once a week, with money and job worries being the main cause.
Almost a third of respondents said they did not tell anyone of their worries, raising the need to teach young people "coping strategies", said Rethink.
Women seemed most badly affected, with one in three suffering frequent anxiety, compared with one in 10 men.
The YouGov poll of 2,000 adults, 250 of whom were aged 18-24, found 33% of young women felt stressed or anxious most days or every day.
Money worries were given as the main reason by 45% of respondents, followed by 33% having concerns about job prospects and 29% worried about pressures from school or university.
Some said they would seek advice or support from a partner or friend, but almost one third (31%) say they kept stress and anxiety to themselves.
James Gorman, Rethink National Young Persons' Programme Manager said the pressures on young people were "huge".
"With the number of young people not in education or employment rising, it's no wonder many are feeling the strain.
"It is extremely important that we teach young people strategies for coping with stress and protecting their mental health.
"Failure to get the right help at the right time can have lasting consequences.
"The longer people suffer in silence, the harder it is to help them recover."
Lucie Russell, Young Minds campaigns director, said the survey suggested young people felt really stressed much of the time.
"It is worrying that young people are unable to speak openly about their anxieties.
"Young people should be taught coping strategies early on at school and at home, so they can deal with difficult feelings and situations.
"But there must also be readily available support both at school and in the community, so that young people don't have to suffer alone."
Paul Farmer, chief executive at Mind said young people were bearing the brunt of the recession.
"Employment is scarce and without a job, anxiety, low self-esteem and unhappiness can set in.
"Unfortunately, stigma around mental health is particularly bad amongst adolescents, which means they tend to bottle things up rather than seek support."