Mladic told the judge he is a gravely ill man and refused to enter pleas to the charges.
According to his attorney, Mladic has been battling cancer and was treated at a Serbian hospital in 2009.
Mladic appeared unable to fully use his right hand. Court guards supported him as he stood up and helped him put on a headset so he could listen to a simultaneous translation of the hearing in Serbian. His head was almost entirely bald after he removed a baseball cap he wore when he entered court and his speech was slow and appeared slightly slurred.
He is charged with the 1995 murders of 8,000 Muslim men and boys in the worst massacre of civilians in Europe since World War II.
The judge scheduled a new hearing for July 4. If Mladic again refuses to plead to the 11 charges, including genocide and crimes against humanity, judges will file "not guilty" pleas on his behalf and preparations will begin in earnest for a trial expected to last years.
The Associated Press contributed to this story.