The trial of Ibrahim Halawa has been postponed until 9 January 2016.
The 20-year-old Dubliner is being tried alongside more than 490 other people.
His mother and one of his sisters are in Egypt but were not allowed inside the courtroom.
In Dublin, his sister Somaia said she was very disappointed that the trial had been postponed yet again and she is very worried about the well-being of her brother.
Mr Halawa was arrested by the Egyptian army as he took refuge in a Cairo mosque while Muslim Brotherhood protesters staged a "day of rage" outside in August 2013.
Minister for Foreign Affairs Charlie Flanagan said he is extremely disappointed by the further adjournment of the trial.
He said he is also worried by reports that the lawyers involved have collectively withdrawn from the case and has expressed his concern about the length of Mr Halawa's detention to the Egyptian government.
Mr Halawa said the case is receiving "high priority" in his department and officials from the Irish Embassy in Cairo were at today's hearing.
Mr Flanagan said Embassy officials visited Mr Halawa on 23 November.
He said there is ongoing contact between the Taoiseach and Egyptian President Abdel Fattah al-Sisi and the Egyptian government "is in no doubt as to the Irish Government's strong interest in Mr Halawa's welfare and our wish to see him released".
Executive Director of Amnesty International Ireland Colm O'Gorman said the organisation is "gravely concerned" for Mr Halawa's mental and physical well-being and called for his immediate and unconditional release.
Mr Halawa faces a possible death penalty and has been imprisoned for more than 28 months without trial.
Mr O'Gorman said he is one of 494 defendants facing a "grossly unfair mass trial which makes it almost impossible for his lawyers to mount a meaningful defence".
