The World Trade Organization (WTO) has ruled that the European Union (EU) flouted global trade rules in its ban on beef treated with growth hormones.
The US hailed the ruling in the long-running trans-Atlantic spat as an "important victory".
But the WTO also found fault with US and Canada because of sanctions they imposed on EU exports in retaliation for the beef ban.
The EU says beef treated with certain hormones poses a health risk.
But the WTO dispute settlement panel said that the EU's justification for its import ban was not backed up with scientific evidence.
It also said that the US and Canada were wrong to extend retaliatory measures on exports of European products such as Roquefort cheese, truffles and Dijon mustard.
The dispute dates back over a decade and has marred trade relations across the Atlantic.
US Trade Representative Susan Schwab said the EU ban was "scientifically unjustified".
"It is high time for the EU to come into compliance with its obligations," she said in a statement.
But the EU demanded that the US and Canada drop their punitive duties on European exports.