The European Court of Human Rights has ruled that Irish abortion laws violated the rights of one of three women who sought terminations in Britain.
The woman, who was in remission for a rare form of cancer, feared it might return as a result of her pregnancy.
While abortion in the Republic is technically allowed if a woman's life is at risk, the court said that was not made possible for the woman involved.
But it ruled two other women in the case had not had their rights breached.
The court said the Irish government had failed to properly implement the constitutional right to abortion if a woman's life was in danger.
Correspondents say the ruling is likely to force the Dublin government to introduce new legislation or bring in new guidelines.
Irish Prime Minister Brian Cowen said politicians now needed to consider the implications of the ruling.
"It's an issue for the whole political spectrum to consider," he said.
Respect for private life
The first two women in the case were a single mother who had other children in care and a woman who did not want to become a single parent.
All three women said they had suffered medical complications on returning to the Irish Republic and said they believed they had not been entitled to an abortion under Irish law.
They all complained that Irish restrictions on abortion had stigmatised and humiliated them, risking damage to their health.
However the third woman had argued that even though she believed her pregnancy had put her life at risk, there was no law or procedure for her to have her right to an abortion established.
The court said that the government in Dublin had breached the third woman's right to respect for her private life by its "failure to implement the existing constitutional right to a lawful abortion in Ireland".
It ruled that "neither the medical consultation nor litigation options, relied on by the Irish government, constituted effective and accessible procedures which allowed the third applicant to establish her right to a lawful abortion in Ireland".
The court said that the only non-judicial way of determining the risk to a woman's life - on which the government relied - was an ordinary medical consultation between the woman and her doctor. It described this as "ineffective".
It said that women and their doctors both ran a risk of criminal conviction and imprisonment "if an initial doctor's opinion that abortion was an option as it posed a risk to the woman's health was later found to be against the Irish constitution".
The court said Irish constitutional courts were not appropriate for determining whether a woman qualified for a lawful abortion.
Under Irish law, abortion is a criminal act although a referendum in 1983 amended the constitution acknowledging the mother's right to life was equal to that of the child.
Following several legal cases, the Irish Supreme Court ruled in 1992 that abortion was lawful if the mother's life was at risk.
However, the Irish parliament has never enacted legislation regulating the constitutionally guaranteed right.
The three women were all supported by the Irish Family Planning Association. They have not been identified, although two are Irish nationals and one is a Lithuanian who is resident in the Irish Republic.
The UK-based abortion charity BPAS - which submitted written observations to the court - welcomed the ruling.
"The lack of clarity as to when abortion may be lawful in Ireland puts women and doctors in an impossible situation, and the sooner this can be remedied the better," said BPAS chief executive Ann Furedi.
Reaction from Irish readers
This is a very welcome ruling. The law on abortion is a breach of the human rights of every Irish woman in both Northern Ireland and the republic. The Irish Family Planning Association estimates that at least 143,479 women travelled abroad for abortions between 1980-2009. Couple this with the 70,000 women in Northern Ireland who have travelled to Great Britain since 1967 for terminations and it is very easy to see that new legislation is needed. Cat McG, Belfast, Northern
As a woman who believes that many people are sadly either anaesthetised or misinformed about the true nature of abortion, I feel grateful to be living, for the time-being anyway, in a country that does not allow abortion on demand. To those who argue for abortion on the grounds of the mother's health, I would point out that statistically, Ireland is one of the safest countries in the world in which to have a baby. The isolation, worry and stress of an unplanned pregnancy can never be ignored or underestimated, but there are still those of us for whom abortion is not just an unpleasant, distasteful solution to a problem, but the deliberate, and in late abortions, cruel, ending of a life, and therefore morally and philosophically wrong. This view, incidentally, is not the sole preserve of Christian Ireland, but was a fundamental part of the Hippocratic oath. This is not to say that we do not need clarification on the legal status of abortion in Ireland. Anne-Marie Russell, Wicklow, Ireland
I knew this would happen. As soon as Lisbon was passed, it was obviously only a matter of time. Although the likelihood of Ireland actually doing anything to legalise abortion is extremely slim. Even if the government were to try and legalise it, they would, as far as I remember, have to hold a referendum for it to be turned down, due to Ireland's rather socially conservative population. John S, Dublin
The problem is the European courts cannot compel us to change the law as abortion is illegal under the constitution. It would require a referendum to change the law. Ted Trim, County Meath
Surely the purpose of a Court of Human Rights is to protect the most vulnerable and the voiceless in society. Is it right to accept that the women in question are more valued citizens in Europe than their unborn children? The people of Ireland have chosen to protect the children and Europe should respect our democratic process. Everyone has the right to life. Antoinette Victory, Dublin
Surely it is up to the woman to decide whether or not she has a termination. You hear of horror stories of women who can't afford to go to England and are forced to have illegal abortions performed by unqualified people. A lot of laws like this in Ireland are based on the Catholic Church's beliefs and are crazy laws in the modern era. Paul, Dublin
I think it's about time. What these women went through was horrible and I am ashamed to be Irish because of it. Chris, Dublin
The Catholic Church has for too long put a stranglehold on Irish law. The abortion referendum 'No' vote was won by the narrowest of margins (for the third time). It puts more lives at risk, since women still travel to the UK for the abortion, the problem does not go away, it just moves the problem elsewhere. Jude Bradley, Dublin
Life is absolutely precious to the unborn as well as to the living. When a child is conceived it has the same rights as everyone else. The time to make decisions about children is prior to conception. Jim, County Limerick
It is simply a disgrace that women - and couples - cannot choose of their own will. This is another example of how the Church has brainwashed people for centuries and does it ring any bells that the Church is ruled by men? I hope Ireland - and any other country against abortion - is forced to follow simple civil rules. David, Killarney, Kerry
This ruling will make the government change the Constitution and allow for abortion in cases of serious health situations of pregnant mothers. I think most reasonable people will be totally against abortion on demand, as is the case in the UK and several other European countries. Jimmy Grisewood, Navan