Former Bosnian Croat General Tihomir Blaskic, jailed for war crimes and ethnic cleansing, has had his sentence reduced from 45 years to nine.
Blaskic has already served eight years in detention
Appeals judges at the war crimes tribunal at The Hague also quashed most of the charges against him.
Blaskic, 43, was convicted in 2000 in connection with a massacre in central Bosnia, in which about 100 Muslims were killed by Croat forces in 1993.
His 45-year sentence was among the harshest handed down by the tribunal.
Former Bosnian Serb General Radislav Krstic is currently appealing against a 46-year jail term for genocide at Srebrenica and municipal official Milomir Stakic is serving a life sentence over the persecutions of Bosnian Muslims in the Bosnian town of Prijedor.
Blaskic was commander of the Croatian forces when Bosnian Croats and Bosnian Muslims were fighting between 1993 and 1994.
The reduction in sentence means Blaskic may serve only a few more months in custody, once the time he has already served has been taken into account, and he takes up his right to apply for early release.
He was cleared of all but three of the 19 counts against him, including convictions for
ordering the attack on the town of Ahmici and being responsible for troops that committed the atrocities.
Around 100 Muslims were killed by Croat forces in Ahmici
Family and friends in the public gallery applauded as the ruling was given.
UN court spokesman Jim Landale said Blaskic would have to apply for early release if he wanted to be set free before he had served the full nine years.
Tribunal judges upheld convictions for illegal detainment and inhumane treatment of prisoners.
They said the appeal followed "an enormous amount of additional evidence" due to the lack of co-operation on the part of the Republic of Croatia before the death of former president Franjo Tudjman in December 1999.
Archive material was only made available after Tudjman's death.