Radovan Karadzic has asked to be released from detention pending his appeal at the International Criminal Tribunal for the former Yugoslavia.
The former Bosnian Serb leader was sentenced last month to 40 years in jail for war crimes including the genocide of more than 8,000 Muslims.
The 70-year-old Karadzic requested the tribunal hearing on April 6 because he said detention was ruining his health.
Karadzic said his health had declined during the eight years he had spent in custody, something he blamed on a "malignancy" in the detention unit which he said had already claimed the lives of other detainees.
Conditions there were "19th-century, like some communist or Turkish prison," he said.
The head of the tribunal turned down his request but ordered that health conditions at the UN detention unit in the Dutch seaside resort of Scheveningen be looked at.