The decision comes from the Administrative Court of Appeals in Stockholm, reports the Pointlex legal news service.
Both the Swedish Tax Authority and the County Administrative Court had earlier denied parents the right to name a child after the famous coloured building blocks for children.
Both referenced an earlier ruling which forbid the name Ikea.
In Sweden's name law, however, there is no written prohibition against using a brand as a first name.
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And the parents, who have called their boy Lego for the past year, say that if the name had entailed any embarrassment, they would have considered changing the name.