A charity warns that an increasing number of young adults are suffering from 'anxiety overload'.
A survey of 2000 adults showed that 66pct agreed to feeling stressed or anxious at least once a week.
Nearly a third said that they did not tell anyone about their worries, raising the need to teach young people "coping strategies", said Rethink.
It was followed that concerns about job prospects with 33pct and 29pct worried about pressures from school or university.
In the survey, women seemed to be most badly affected.
One in three agreed to suffering from frequent anxiety, compared with one in 10 men.
The YouGov poll of 2,000 adults, 250 of whom were aged 18-24, found 33pct of young women felt stressed or anxious most days or every day.
Some said they would seek advice or support from a partner or friend, but almost one third say they kept stress and anxiety to themselves.
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," BBC News quoted her as saying.
"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," she added.
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," he added.