The former Yugoslav president had been scheduled to begin the long-awaited presentation of his defense on Wednesday, after three earlier postponements.
Judges at the U.N. tribunal for the former Yugoslavia said he is still too sick and will review the status of his health on July 19, tribunal spokesman Jim Landale said.
"On the basis of the blood pressure values of the accused it was found he should rest," Landale said. "Clearly he is not well enough to start on Wednesday."
Landale did not give figures, but a doctor's report submitted earlier this month showed that at times of stress, Milosevic's blood pressure rises to 200/130 and falls to around 140/80 when he is relaxed. A normal reading is 120/80.
Milosevic, 62, has been on trial since February 2002, facing 66 counts of war crimes for the Balkan wars of the 1990s. The trial has been severely set back by his heart trouble, exhaustion and bouts with flu. It was further delayed by the resignation in February of presiding judge Richard May due to health reasons. May died earlier this month.
His defense case was initially scheduled to begin on June 8.
Milosevic has been allotted four hours to present an opening statement, likely to span two court sessions. He will then be able to call witnesses and present evidence.
Milosevic wants to call 1,400 witnesses, including British Prime Minister Tony Blair and former President Bill Clinton. The judges will have to cut the witness list if Milosevic is to complete his presentation within the 150 days allowed by the court.
Despite pressure from prosecutors, Milosevic has refused to take on a defense lawyer. The tribunal has allowed Milosevic to represent himself, but said last week it may have to appoint a defense lawyer against his will due to his health problems.
According to a July 2 health report, Milosevic has suffered "organ damage" due to high blood pressure, including "hypertrophy of the left ventricle," meaning an enlargement of the main pumping chamber of the heart.
Milosevic, who doesn't recognize the tribunal, has been assisted by three Belgrade lawyers who help him gather evidence and review court materials.
Milosevic is charged with crimes against humanity, grave breaches of the Geneva conventions, and violations of the laws or customs of war on three separate indictments, pertaining to the conflicts in Bosnia, Croatia and Kosovo.
In Bosnia, he is charged with overseeing "the widespread killing of thousands of Bosnian Muslims during and after the take-over of territories within Bosnia and Herzegovina," and "the killing of thousands of Bosnian Muslims in detention facilities within Bosnia and Herzegovina."
He is accused of, "the extermination or murder of hundreds of Croat and other non-Serb civilians, including women and elderly persons" in Croatia.
In Kosovo, prosecutors allege that Milosevic "planned, instigated, ordered, committed or otherwise aided and abetted in a deliberate and widespread or systematic campaign of terror and violence."
"Kosovo Albanians were frequently intimidated, assaulted or killed in public view to enforce the departure of their families and neighbors," the indictment reads. "Many Kosovo Albanians who were not directly forcibly expelled from their communities fled as a result of the climate of terror created by the widespread or systematic beatings, harassment, sexual assaults, unlawful arrests, killings, shelling and looting carried out across the province."