The judge, Marine Col. Keith Parrella, would be leaving the base, said Ronald Flesvig, a spokesman for the Guantanamo military commission. He did not disclose details of the medical issue that ended what had been planned as a weeklong hearing.
Parrella had been scheduled to hold a hearing behind closed doors Wednesday to take testimony from a former CIA interpreter at a clandestine detention facility where at least two of the five defendants had been held under what the government called its "enhanced" interrogation and detention program. Defense lawyers argued unsuccessfully Tuesday to have the hearing remain open.
The judge's departure was the latest of many delays in long-stalled proceedings against Khalid Shaikh Mohammad, who has portrayed himself as the mastermind of the Sept. 11, 2001, terrorist attack, and four co-defendants.
The five were arraigned in May 2012 before a military commission on charges that include terrorism and nearly 3,000 counts of murder in violation of the laws of war for their alleged roles helping to plan and providing logistical support to the plot. They could get the death penalty if convicted.
A trial date has not been set. The next pretrial hearing will be in March at the base in Cuba.