A father of at least 550 children has been banned from donating any more of his sperm after he "deliberately lied" to prospective parents.
National guidelines in the Netherlands say sperm donors are allowed to father a maximum of 25 children with 12 mothers.
The prolific donor, identified only as Jonathan M under Dutch privacy rules, provided sperm to several Dutch fertility clinics, a facility in Denmark and people he met through advertisements and online forums, the Hague District Court said in a written judgement.
His lawyer said his client wanted to help people who would otherwise be unable to conceive.
But the judge who heard the civil case said the donor "deliberately lied about this in order to persuade the parents to take him as a donor," according to a statement from the court.
The court added the parents of the children are "now confronted with the fact that the children in their family are part of a huge kinship network. with hundreds of half-siblings, which they did not choose".
This "has or could possibly have negative psychosocial consequences for the children," it said.
It added: "It is therefore in their interest that this kinship network is not extended any further."
The case was about "conflicting fundamental rights," the court's statement said.
"On the one hand, the right to respect for the privacy of the parents and the donor children… and on the other hand, the same right of the donor," it added.
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The court ruled that "the interests of the donor children and their parents outweigh the interest of the donor in continuing to donate sperm to new prospective parents".
The injunction was sought by the mother of a child conceived with the donor's sperm and a foundation representing other parents.
It was handed down by a Dutch court on Friday.
The mother, identified by the foundation only as Eva, said: "I hope this ruling leads to a ban on mass donation and spreads like an oil slick to other countries.
"We must stand hand in hand around our children and protect them against this injustice."
The donor faces a €100,000 (£88,115) fine per case if he breaches his ban.
Lawyer Mark de Hek called the ruling a "clear signal and, as far as I am concerned, a final warning to other mass donors".