A "yes" vote would overturn the eighth amendment that effectively bans terminations at present
People in the Irish Republic were heading to the polls on Friday to vote in a divisive referendum on abortion.
Under the eighth amendment, termination is only allowed when a woman's life is at risk. Rape, incest or fatal foetal abnormality are not considered grounds for abortion.
A 'yes' vote would repeal the eighth amendment that was introduced after a referendum in 1983.
Campaigning on both sides has been robust and passionate. Ireland has a strong Catholic tradition of clerical influence but that has diminished in recent decades.
The country voted overwhelmingly for same-sex marriage in 2015.
But abortion is a more emotive issue and the key to the outcome of this poll could depend on which side is more motivated to get out and vote.
Around 3.2 million people are registered to vote and more than 100,000 new voters registered ahead of the poll.
Voting can take place until 2300 CET on Friday and the result is not expected until late Saturday. Exit polls indicate a close result with the possibility of a recount in places.