By the narrowest of votes late on Wednesday night, the US House of Representatives gave the go-ahead for the island's 3.8 million people to decide whether they want statehood, independence or a continuation of "US commonwealth" status - effectively as a US colony.
Since polls suggest less than 5 per cent of islanders want to go it alone - they currently have US citizenship and rely almost totally on trade and other ties with the US - the referendum would probably be close between those who want statehood and those who prefer the status quo.
Although the House bill proposed a referendum this year, it first requires a further vote in the Senate. This seems unlikely before the end of 1998. And even if the referendum were to go in favour of statehood, it could take 10 years for the transition to be made and the extra, 51st star to be added to the Stars and Stripes flag.
Puerto Ricans reacted cautiously to the heated 12-hour House debate on television, culminating in a 209-208 vote. The statehood issue has split the island and most are wary of decisions taken in the US, where islanders cannot vote. They have no voting representatives in the US Congress and do not pay federal taxes either, though they are subject to the US military draft.
The independence question led to violence on the island in the Fifties. Puerto Rican independence militants opened fire in the US House of Representatives in 1954, wounding five congressmen. Four years earlier, Puerto Rican nationalists had tried, unsuccessfully, to kill President Harry Truman.
Many islanders were upset by this week's debate, when the right-wing Republican congressmen tried to push through an amendment that would have made English Puerto Rico's only official language. Most Puerto Ricans speak only Spanish and less than a quarter are bilingual.
Squeezed between the island of Hispaniola to the west and the former British and other Caribbean islands to the east, the majority of Puerto Ricans accept they could not live without American aid. The island receives $10bn (pounds 6bn) from the US budget each year, which may rise to $14bn if it becomes a state.
In a non-binding plebiscite five years ago, more than 48 per cent of islanders voted for the status quo, more than 46 per cent for statehood and about 4 per cent for independence. Under the terms of the House bill, a simple majority of over 50 per cent would be necessary.