The trial of Ibrahim Halawa has been postponed for the 16th time in Cairo, Egypt, until 13 December.
The 20-year-old Dublin man has been detained by Egyptian authorities since he was arrested at a protest in August 2013.
This is the 16th time the mass trial, involving 494 defendants, has been adjourned.
Mr Halawa's solicitor, Darragh Mackin, said the trial had been postponed due to the non-appearance in court of a number of defendants.
Minister for Foreign Affairs Charlie Flanagan has said that he is concerned and frustrated at the latest delay in the trial of Mr Halawa.
In a statement, the minister said: "Our priority remains to see this young man returned to Ireland and to his family as soon as possible.
"In light of today's developments, we will be pursuing further contacts at the highest levels with Egypt to address Mr Halawa's continued detention and to again call for his immediate return to Ireland."
Mr Flanagan contacted Egyptian Ambassador SohaGendi to express his concerns regarding the latest adjournment.
Amnesty International has condemned the latest postponement of the trial.
In a statement, it said: "The continuing imprisonment of this young Irish citizen is a violation of both international and Egyptian law.
"We reiterate our call for his immediate and unconditional release and urge the Irish Government to continue their work on his behalf and to use every means at their disposal to secure his release."
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