The number of people in their 20s living in Ireland has declined by more than a quarter.
The latest statistics from the CSO show the age bracket has dipped by more than 200,000 in the last six years, to just under 550,000 in 2014.
There has been a particularly notable decrease in the number of 20-24 year-olds - down 31%.
The figures were released as part of the CSO's Vital Statistics Yearly summary, released last week.
Economist with Independent Newspapers Dan O'Brien has been interpreting the figures, saying he was surprised when he first saw them. He spoke to the Sunday Show here on Newstalk to discuss them in depth.
"When I looked at this first, I thought OK this is to do with emigration." he said. "But then when you look more closely at it it shows that emigration only accounted for about 70,000 loss of twenty-somethings.
"Most of it results from something that happened decades ago, and that was in the 1980s very suddenly the number of babies born in Ireland started to fall quite rapidly - and it continued to fall until the mid-90s," he explained.
Sociologist and writer Niamh Hourigan also spoke to the show about some of the potential social impacts of such a change.
"One of the long term consequences in terms of societies with an ageing population is the idea that you have a sort of complacency and stagnation," she pointed out. "But one of the things that came out in a UCC report on the Irish emigrants... is that actually a lot of the emigrants who are going are very engaged with Irish society." She cited the recent same-sex marriage referendum as an example of this.
"If we look at debates in society like Japan or France at the moment... demographic issues are front and centre in terms of how economic and social policy are managed", Niamh explained, and said the issues need to be more prominent in discussions and actions here in Ireland.
You can listen back to her thoughts below: