A 21-year-old woman with Down's Syndrome should not be sterilised, a High Court judge has ruled.
Mr Justice Cobb concluded that sterilisation would be "disproportionate" - following a hearing at the Court of Protection in London - despite opposition from the woman's parents.
He said the woman lacked the capacity to understand and weigh up options and said the case engaged important human rights considerations.
The judge said he had made a declaration under the provisions of mental capacity legislation after the woman's parents disagreed with a local authority - and medics - about the best way "to achieve contraception". He said no party involved should be identified.
The judge said the local authority and medics opposed sterilisation after commissioning a report from a specialist. They thought that sterilisation was "not the least restrictive option". Mr Justice Cobb said the woman's parents disagreed and thought that "in reality, it is".
The judge said the local authority had begun proceedings in the Court of Protection, which is part of the High Court and analyses issues surrounding the care and treatment of sick and vulnerable people. And he said it was in the woman's best interests that he should "bring as much clarity to medical treatment issues" as he could.
"The issue which divides the parties is whether I should declare in these proceedings at this stage that it is not in the woman's best interests to be the subject of a sterilisation procedure," said Mr Justice Cobb - in a written ruling published following a hearing earlier this month.
"No-one can doubt the seriousness and significance of a sterilisation procedure. Further surgery would be required to reverse it, and then only with a moderate prospect of success."
He added: "I have sought to achieve the right balance between protection and empowerment. It is my judgment that sterilisation would be a disproportionate (and not the least restrictive step) to achieve contraception for the woman in the future."
The judge said risk management was "plainly" better than invasive treatment and less restrictive. He said there were less restrictive methods of "achieving the purpose of contraception" and if contraception became necessary they should be tried.