Nearly 2,400 fewer pupils took the exam this summer, down almost a fifth on last year's entry of 12,185, according to figures published yesterday. The fall was only partially compensated for by just over 1,000 more entries for the second-language short-course GCSE.
French and German also saw significant falls, despite attempts to boost modern foreign languages in primary schools. But pass rates for all three languages were better or on a par with last year.
Teachers have warned that pupils are being put off Welsh by the new second-language GCSE course, which involves more continuous assessment, oral, aural and reading tests. UCAC, the Welsh-medium teachers' union, said the fall in entries was worrying, and called for a full review of the subject. ACCAC, the Welsh qualifications, curriculum and review authority, is considering 115 responses to a consultation on the new course.
Mal Davies, head of Willows high school, Cardiff, said the course was "extremely demanding", and highlighted problems recruiting Welsh teachers.
Gareth Pierce, chief executive of the WJEC, the Welsh exam board, said:
"It's vitally important all pre-16 students receive a very positive experience of Welsh second language. If the curriculum or assessment doesn't provide that, it seems it's a high priority for action."
Meanwhile, "sexy" subjects such as media studies are pushing out modern foreign languages, according to CILT Cymru, the Assembly-funded national centre for languages.
The organisation has been piloting language lessons for Year 5 and 6 children in primary schools since 2003-04, but says it will be several years before they affect GCSE entries.
More needs to be done to sell languages to young people, according to Ceri James, director of CILT Cymru: "Pupils seem to be put off taking languages because they appear harder. But if you look at the results, more pupils attain A*-C passes in modern foreign languages than maths, English and history."
* More young people studying the intermediate-level Welsh baccalaureate completed their studies and collected the award this summer, according to figures released with this week's GCSE results.
Completion rates rose from 30.6 to 47.8 per cent, and the proportion receiving the full intermediate diploma rose from 13.7 to 50.2 per cent.
Jason Hicks, Welsh bac co-ordinator at Barry comprehensive, Vale of Glamorgan, said pupils' reservations about the course had been overcome and those pupils who might otherwise have left for further education colleges had been successfully targeted.
Education minister Jane Davidson said the intermediate bac results were very encouraging and showed lessons were being learned from the pilot.