Lesbian parents have the same rights and responsibilities towards their children in the event of a break-up, California's highest court has ruled.
Lesbian parents will have custody and visitation rights
The ruling came in three separate cases involving lesbian parents who conceived under differing donor circumstances.
The court decreed that despite their differing circumstances each woman had custody rights and monetary obligations just as parents of the opposite sex do.
The decision comes as a bitter debate over gay marriage rages in California.
Methods of conception
In two of the cases two lesbians were living together and had a child after one of the partners donated an ovum to the other, who was then artificially inseminated.
The women were raising the children together, but when they broke up in each case the mother who bore the child wanted to be considered the legal mother.
In the third case a lesbian couple, listed as Elisa B and Emily B, were living together and decided that they should both become pregnant by an anonymous donor.
It was agreed that Emily B would stay at home to raise the couple's three children, but when they later split Elisa tried to argue that she should not have to pay maintenance for Emily's biological children.
A panel of state Supreme Court justices ruled for the first time that those laws which hold estranged fathers to account should also apply to gay and lesbian couples who have children together.
Three years ago the same court ruled that men who take on the role of a father figure can become legal fathers even of they are not the biological parents.
"These legal principles apply with equal force in this case," Justice Joyce Kennard said.
Being a legal parent "brings with it the benefits as well as the responsibilities," she added.
"The court is now protecting the children of same sex parents in gay families in the same way children are protected with heterosexual couples in heterosexual families," said Jill Hersh, a lawyer for one of the women.
The rulings come amid controversy over whether gay marriage should be legal in California.
San Francisco started issuing marriage licences to same-sex couples in February 2004, after the city's new mayor decided to defy state law and allow gay weddings.
More than 3,400 gay couples got married before California's Supreme Court ordered a halt the following month.