The proportion of A-levels scoring at least an A grade has fallen for the first time in more than 20 years, official figures showed today.
In total, 26.6% of the exams were given an A or A*, down from 27% in 2011 - a record drop of 0.4%.
It is believed to be the biggest fall in the history of A-levels. The last time it dropped was between 1990 and 1991 when it decreased to 11.9% from 12%.
The pass rate at A grade also stalled in 1996 and 1997, when 15.7% of exams were awarded at least an A.
Today's figures, published by the Joint Council for Qualifications (JCQ), also show that fewer A-level exams achieved an A* this year.
Around one in 12 (7.9%) exams were given the top grade, which is awarded for the third time this summer, down from 8.2% in 2011.
Boys overtook girls at A* grade for the first time, with 8% of boys' entries attaining the top mark, compared to 7.9% of girls'.
Today's figures also show that the overall A* to E pass rate has risen for the 30th year in a row.
Some 98% of exams achieved at least an E, compared to 97.8% last year.
Around 335,000 students in England, Wales and Northern Ireland are receiving their A-level results today.
But while many will be celebrating, others still face a scramble to secure a university place.
Initial figures from UCAS show almost a 7% drop in the numbers of students who have already had their places confirmed.
Michael Turner, director of the JCQ, which represents exam boards, said: "Today is about celebrating the successes of our young people and recognising the hard work that has gone in to achieving these results.
"They, and their teachers, can be proud of their achievements.
"The STEM subjects continue to rise, with mathematics, biology, chemistry and physics all in the top 10 most popular subjects.
"Over the next few years, it will be interesting to see if, with the existence of the English Baccalaureate, the continued decline in students taking a foreign language is reversed."
Brian Lightman, general secretary of the Association of School and College Leaders, said the drop in A grades was a "minor fluctuation".
He said: "The important point here is, if you look at the trend of improvements in schools, the numbers now succeeding at GCSE and accessing A-levels has been a success story of our education system."
Mr Lightman added that there were more people taking A-levels this year and large numbers of students getting "very good results", and that the fall in the very top grades was not significant.
He said: "All of these trends are positive. The minor fluctuation is not a significant issue to worry about.
"It is a minor fluctuation which you will get in a system that has so many millions of entries each year."