Paul Clarke from St Paul's College, Raheny, has been named overall winner of the 50th BT Young Scientist and Technology Exhibition with Cathy Hynes and Eve Casey of Kinsale Community School named as Best Group winners.
The winners were announced at a ceremony in the RDS this evening.
The winning entry, "Contribution to Cyclic Graph Theory", was carried out by Paul Clarke, a 17 -year-old fifth year pupil.
Late last year, he also won another major national science competition, Scifest.
Paul's project involved a study of graph theory, the mathematical theory of the properties and applications of graphs.
Graph theory can be applied in any area of science where things happen in pairs.
For example, in molecular chemistry graph theory is used to model the structure of a molecule.
It can also be used in computer applications where it is used to model complex computational problems.
The Best Group award went to 13-year-old Eve Casey and 12-year-old Cathy Hynes, both first year pupils at Kinsale Community School in Cork, from where last year's winners also came.
Their project was titled: "A study using statistical methods of people's attitudes to the ageing workforce of the future".
Their survey of 1,147 found that 63% of respondents felt younger than they were, and 17% felt older, with the remaining 10% feeling their actual age.
The average age at which respondents would like to retire was 59.7, but respondents thought they would actually retire at 65.5.
Eve and Cathy have won a trophy and a cheque for €2,400.
550 projects involving more than 1,200 students were vying for the top prize.
Organisers said the standard of the projects is the highest they have ever seen, particularly at senior level where there are more Leaving Cert students taking part than ever before.
More than 120 awards were presented at this evening's prize giving, including special awards, category awards, gold and travel awards and the top four.
Thousands of school children, teachers, parents and other members of the public have been visiting the exhibition since it opened on Wednesday.
Organisers, who predicted that more than 40,000 would visit over the four days, said numbers are up on last year.
The winner receives a trophy, a cheque for €5,000 and the opportunity to represent Ireland at the European Union Contest for Young Scientists.
The exhibition is open to the public tomorrow, when retired Canadian astronaut Chris Hadfield will be visiting.