The proportion of A-levels scoring the highest grades has risen for the first time in six years, although figures suggest a major government overhaul of exams is having an impact on results.
Boys emerged as the winners in this summer's results, pulling ahead of girls in terms of A*-A grades for the first time in almost two decades.
The results come as early Ucas data shows a 2% drop in the number of students accepted on to UK degree courses for this autumn, compared to the same point last year.
Despite the fall, the number of students gaining university places on A-level day is still the second-highest number recorded, with 416,310 people accepted, the university admissions service said.
National figures for England, Wales and Northern Ireland show more than one in four (26.3%) A-level entries scored an A* or A this summer, up 0.5 percentage points on 2016.
It is the first time the A*-A pass rate has risen since 2011.
The increase comes amid major changes to the qualifications with a move away from coursework and modular exams throughout the course in England, as well as the decoupling of AS-levels, making them more challenging for students.
While the A*-A pass-rate has risen, there has been a drop in top results among the first 13 subjects to be overhauled in England, statistics from the Joint Council of Qualifications (JCQ) show.
When comparing 18-year-olds' results for these subjects, the proportion of A* grades for these courses is down 0.5 percentage points to 7.2% from last year, A*-A grades have dropped 0.7 percentage points to 24.3% and A*-E results have fallen 0.5 percentage points to 98.1%.
The 13 reformed subjects are art and design, biology, business, chemistry, computer science, economics, English language, English language and literature, English literature, history, physics, psychology and sociology.
Alex Scharaschkin, director of research at AQA, said students will not have been disadvantaged by taking the new-style exams.
"We've been clear and very careful to make sure that the results are fair, so there has been no advantage or disadvantage from something you cannot control, the year you were born," he said.
Exam boards suggested the fall could be influenced by several factors including lower prior attainment for students taking these subjects this year.
Mark Bedlow, OCR's director of regulation: "The changes and the results we're seeing in the reformed subjects year on year are not abnormal and can really be ascribed to changes in students' abilities based on their prior year attainment.
"There may be other factors at play as well.
"For example, in the reformed A-levels, poorer performing students will not have been filtered out for having performed poorly at AS-levels.
"Many of those sitting reformed A-levels will be doing so without having sat AS-levels first."
In previous years, sixth-formers would have used their AS-level grades at the end of the first year of their course to decide whether to continue with the subject to full A-level.
Geoff Barton, general secretary of the Association of School and College Leaders (ASCL), said the reformed qualifications are now more challenging in terms of their structure than in their content.
AS-levels no longer count towards final A-level grades in reformed qualifications.
"I don't think the difficultness is necessarily in the change of content it is in the way they are being assessed," Mr Barton said.
"It's the fact that you haven't got a staging post at the end of Year 12, or as you had a few years ago, modules at the end of each term."
The figures, published by the Joint Council for Qualifications (JCQ), reveal that boys have pulled ahead of girls for the first time in terms of A*-A grades, and have widened the gap at the highest result alone (A*).
In addition, the data shows:
:: The overall A*-E pass rate has fallen by 0.2 percentage points to 97.9%;
:: The proportion of entries awarded the highest result, A*, has risen 0.2 percentage points to 8.3%.