The 82-year-old was to be summoned for questioning over corruption allegations, abuse of power and violence against protesters during the 18-day uprising that forced him out of office.
Mubarak's two sons were also summoned and were being questioned at the prosecutor's office in the provincial capital of El-Tor.
Dozens of demonstrators picketed the hospital, denouncing the president and carrying a sign reading "Here is the butcher." They scuffled with supporters of Mubarak amid a massive security presence.
Several hundred protesters remain in Cairo's barricaded Tahrir Square, calling for an investigation into the military's use of violence against them. Early Saturday, soldiers forcefully stormed a protest camp to break up a sit-in, killing at least one demonstrator and wounding dozens.
Following that attack, protesters started a new sit-in at Tahrir Square, demanding the resignation of the minister of defense and head of the army.
The Associated Press contributed to this report.