Under the Civil Code, a baby whose mother became pregnant while she was married is presumed to be that of the husband, and a child born within 300 days of the mother's divorce is legally considered to be that of the ex-husband. A lawsuit to deny the legal paternity can only be filed by men.

If a women who escaped from an abusive husband but is still legally married has a child with another man, and does not wish to have the baby registered as that of her legal husband, she has no recourse but to contact the husband and ask him to take the active step to deny his paternity. If the woman wants to avoid any contact with the husband, she might choose not to register the baby's birth with the authorities. A child born without entry in the family registry faces various disadvantages in life, such as being unable to obtain a residency certificate, health insurance card or passport. The Justice Ministry confirms that there are at least 715 people nationwide who lack family registry. But that number is widely believed to represent only the tip of an iceberg.

The Osaka High Court last week turned down a suit filed by a Kobe woman in her 60s, her daughter and grandchildren who argued that the Civil Code provision allowing only men to take steps to deny legal paternity is unconstitutional. But while the court upheld the lower court ruling dismissing the plaintiffs' demand for damages from the government for the losses they incurred due to the provision, it said the issue of people without family registry should be "left to the legislative discretion of the Diet."