Ireland's population is expected to grow to more than five million within 15 years if current rates of births, deaths and migration continue, according to the Central Statistics Office.
In its Population and Labour Force Projection report for 2006-36, the CSO suggests the State will continue to rely on strong inward migration to maintain economic growth.
The number of older people is projected to increase substantially by 2036 with the number of over-65s increasing from 11 per cent of the population to about 20 per cent.
It forecasts that the economy will need 45,000 immigrant workers every year for the next 12 years to sustain economic growth. At present, there is a net influx of 35,000 immigrant workers annually.
Men and women are also expected to live for substantially longer. The life expectancy for men is expected to increase from 75.1 years in 2002 to 82.47 years in 2036.
Women's mortality rate is projected to rise from 80.3 years to 86.86 years over the same period.
Officials in the CSO admitted, however, it was difficult to project with any certainty demographic patterns in the years ahead.
Senior statistician Mr Aidan Punch said in earlier reports the CSO had not predicted the large growth in inward migration from the late 1990s onwards.
"We were seriously out on migration in the 1996-2002 projections. Our bullish assumptions were blown out of the water by what happened in the end," he said.
This report forecast net migration of 115,00 in its highest projections. The real figure was significantly higher at 154,000.
In its projections for 2006-2036, the CSO says it is "very unlikely" the new pattern of strong immigration will be reversed to any sustained degree over the projection period.
It sets out two scenarios, with immigration continuing at a high level or immigration continuing at more moderate levels.
At present, there is an influx of 35,000 immigrant workers annually. The high level projection would result in a net inflow of 22,600 people a year until 2036. More modest projections would result in average inflows of nearly 11,000 over the same period.
The older population, meanwhile, is expected to increase significantly in the years ahead. There were 430,000 over-65s in 2001, accounting for 11 per cent of the population. This figure is expected to increase to 20 per cent, or 1.1 million, by 2036. The number of people aged 80 years or more is projected to treble from a 2001 level of 98,000 to about 320,000 in 2036.
The labour force is projected to increase from its 2004 level of 1.92 million to reach nearly 2.4 million by 2016, assuming current rates of migration continue. This would represent an annual gain of 38,000 people.
The report also points out that there have been dramatic gains in labour force participation of married women in recent years.
However, it says Ireland still lags behind many EU countries and it projects that a "catching up" process will result in the percentage of women in the labour force increasing from 42 to 44 per cent by 2016.
It also projects small increases in the labour participation rates of men aged 55 and over, reflecting a tightening of the labour market supply of young people and the removal of barriers to people continuing to work well into old age.
Ireland's population trends: CSO projections
Total population*
2004: ... 4 million
2016: ... 4.85 million
2021: ... 5.14 million
* Based on strong net immigration
Source: Population and Labour Force Projections, 2006-36
Younger population*
2001: ... 827,000
2016: ... 1,500,000
* People aged 0-14 years
Older population*
2001: ... 430,000 people
2036: ... 1.1 million
* People aged 65 years or older
Migration*
2002-06: 30,000 p.a.
2006-11: 30,000 p.a.
2011-16: 30,000 p.a.
2016-21: 20,000 p.a.
*migration assumptions based on strong net immigration