Some 48.5 percent of Spaniards in this age group are still living with their parents, the figures from Spain's national stats body, the INE, show.
At the same time, more than 2 million Spaniards aged 25–34, or 32.8 percent, are living with their parents.
In the UK, just 26 percent of people aged 18 to 29 are living with their parents, according to the recent European Quality of Life Survey. In Germany, it's 23 percent and in France it's 28 percent.
In fellow crisis-hit Greece, however, the figure is a much higher 46 percent.
The new INE study, based on figures from its recent household survey, also reveals just 14.7 percent of Spaniards aged 25 to 34 live alone.
"It's very hard to leave home in Spain when unemployment rates for young people are around 55 percent," author Sergio Alsonso told The Local recently.
"And those young people who are working are only earning €1,000 ($1,350)," he added.