An Italian law excluding offspring from having the option to be registered under the mother's maiden name was "patriarchal", "discriminatory" and a rights violation, the European Court of Human Rights ruled, ordering it be ended.
The patronymic practice constituted a "difference of treatment between men and women," the Strasbourg-based court said in its judgement.
In doing so, it sided with an Italian couple who have fought for 13 years to have their children carry the wife's maiden name, rather than the husband's last name.
The requirement they stick to the father's surname was an infringement of their private lives, they argued.
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They won a half-victory at the end of 2012 by gaining permission from local authorities to add the mother's name to that of the father's for Maddalena, but that was not sufficient and they took the issue to the European rights court.
While recognising that Italy's legal tradition had its roots in a practice dating back to the ancient Roman era, the court said it was today incompatible with the Italian constitution's principle of gender equality.
Rome will now have to change its legislation to comply with the ruling, unless it lodges an appeal with a higher chamber in the European court within three months.
The parents at the heart of the case expressed their triumph to Italy's ANSA news agency.
Cusan said: "It's a new step forward to progress and it will above all benefit our children."
Several Italian lawmakers, from across the political spectrum, also hailed the judgement as a boost for gender parity.
Some other European countries are already more flexible in the choice of a baby's surname. In France, for instance, a child can carry the last name of the father or the mother, or a combination of both.