A quarter of young people in the UK now live with their parents, official figures show.
The Office for National Statistics (ONS) said more than 3.3 million adults between the ages of 20 and 34 were living with parents in 2013, 26% of that age group.
The number has increased by a quarter, or 669,000 people, since 1996.
This is despite the fact that the number of 20 to 34-year-olds in the UK remains almost the same, the ONS said.
In 1996, the earliest year for which comparable statistics are available, there were 2.7m 20 to 34-year-olds living in the family home - 21% of the age group at that time.
The ONS also found young men were more likely to live at home than women. One in three men live with their parents, compared with one in five women.
London has the lowest rate of 20 to 34-year-olds living with their parents, with the figure at 22%.
Northern Ireland has the highest proportion of young adults living with their families at 36%, followed by the West Midlands at 29%.
The ONS said the size of Northern Ireland means it is more feasible to commute to work or university and remain living with parents than in other parts of the UK.
Also, cohabitation in Northern Ireland is about half as common as in the rest of the UK.
The ONS suggested the trend of living at home might be due to the recent economic downturn.
Karen Gask, senior research officer at the ONS, said: "I think one of the main reasons is housing affordability, and that's been cited by several academics who've looked into it.
"It's hard for young people to get on the housing ladder."
The ratio of house prices paid by first time buyers to their annual incomes has risen from 2.7 to 4.47 in the period from 1996 to 2013, she added.
Miss Gask also said many were delaying settling down with a partner, choosing to stay with family instead.
She added: "There are wider implications for things like fertility rates, as people often look to move out of the parental home before having children."
Other findings from the ONS study include:
- Some 65% of men and 52% of women aged 20 lived at home in 2013
- The figure decreases with age. At 34, 8% of men and 3% of women were living with parents
- The percentage of young people living with their parents who are unemployed was 13%, more than double the unemployment rate of those who live elsewhere, which was 6%
- A total of 510,000 people aged 35 to 64, 2% of the total population in that age group, were living with parents in 2013 - this rate has stayed stable since 1996, the ONS said.