Presiding judge Alphons Orie said he was delaying the Yugoslav war crimes tribunal case due to "significant disclosure errors" by prosecutors, who are obliged to share all their evidence with Mladic's defense team.
He said judges are still analyzing the "scope and full impact" of the error and aim to establish a new starting date "as soon as possible." The presentation of evidence was supposed to begin later this month.
Prosecutors already had admitted the errors and did not object to the delay. Mladic's attorney has asked for a six-month delay.
Earlier, prosecutors wrapped up their opening statement in the trial by recounting in painstaking and chilling detail the systematic murder by Bosnian Serb forces commanded by Mladic of thousands of Muslim men and boys in Bosnia's Srebrenica enclave in July 1995, Europe's worst massacre since World War II.
Exact numbers of the Srebrenica massacre range from 7,000 to 8,000.
"In a period of only five days, from July 12-16, 1995, the armed forces of (Bosnian Serb leader) Radovan Karadzic and Ratko Mladic expelled the civilian population of Srebrenica and murdered over 7,000 Srebrenica men and boys," McCloskey said.
Mladic's army "carried out their murderous orders with ... dedication and military efficiency," he added.
Mladic, the 70-year-old former commander of the Bosnian Serb army, showed no emotion on the second day of his genocide trial as prosecutor Peter McCloskey showed judges a fleeting video of what he said were the bodies executed Muslim men piled in front of a bullet-riddled wall.
On the first day of the trial Wednesday, the court's public gallery was crowded with relatives of the slain men who angrily exchanged hand gestures with Mladic through the bulletproof glass screen separating them.
On Thursday, most of the survivors had left and videos showing a bullish Mladic strutting through the deserted streets of Srebrenica and berating the commander of Dutch U.N. peacekeepers were greeted largely with silence and occasional murmurs.
One woman, Hatidza Mehmedovic, wept in the court's lobby during a break in the proceedings.
"I buried both of my sons and my husband. Now I live alone with memories of my children," she said. "I would never wish even Mladic to go through what I go through. Not Mladic or Karadzic. Let God judge them."
Mladic is accused of commanding Bosnian Serb troops who waged a campaign of murder and persecution to drive Muslims and Croats out of territory they considered part of Serbia. His troops rained shells and snipers' bullets down on civilians in the 44-month-long siege of the Bosnian capital, Sarajevo.
He has refused to enter pleas, but denies wrongdoing. If convicted, he faces a maximum sentence of life imprisonment.
The first witness is scheduled to testify July 29, although that may be delayed due to problems with prosecutors disclosing evidence to Mladic's lawyers.
Mladic fled into hiding after the war and spent 15 years as a fugitive before international pressure on Serbia led to his arrest last year. Now he is held in a one-man cell in a special international wing of a Dutch jail.
But the fact that he is jailed and on trial is seen as another victory for international justice and hailed by observers as evidence that - more often than not - war crimes tribunals get their indicted suspects, even if they have to wait for years.
McCloskey outlined how, after overrunning Srebrenica, Mladic's forces summoned buses and trucks from across Bosnia to transport women and girls out of the enclave and to move captured men to schools and other public buildings. The men were then driven to remote execution locations and gunned down by firing squads and their bodies were plowed into mass graves.
McCloskey said so far the remains - sometimes no more than a couple of bones - of 5,977 victims have been exhumed. He showed photographs of an exposed mass grave to underscore to judges that the victims were not war casualties.