Ireland have slipped to their lowest position since the International Rugby Board's world rankings were launched in 2003.
Ireland's RBS 6 Nations defeat against Italy in Rome on Saturday meant they finished fifth in the championship, above France on points difference.
It also meant they dropped two places to ninth on the latest rankings list published by the IRB.
Six Nations champions Wales remain fifth, just 0.36 points behind fourth-placed England, who had to settle for second place in the championship after a heavy 30-3 defeat in Cardiff.
Elsewhere, Scotland lie 10th, with an unchanged top three of New Zealand, South Africa and Australia.