David Cameron has called on Argentina to respect the wishes of the people of the Falkland Islands to remain British.
The prime minister said the almost unanimous vote in favour of staying a British overseas territory was the "clearest possible result".
He said Argentina should take "careful note" of the referendum, and Britain would always defend the islands.
It follows pressure from Argentina over its claims to the islands, 31 years after the Falklands War with the UK.
Most Argentines regard the islands, which they call Las Malvinas, as Argentine and their recovery is enshrined in the national constitution.
Argentine President Cristina Fernandez de Kirchner has made clear that her country does not recognise the referendum, insisting it has no legal validity.
However, Mr Cameron said the islanders were entitled to the right of self-determination.