In May, 12.7m people in the UK went to the movies, down 19% on the 15.7m who attended in the same month last year.
This fall came despite the release of 'Indiana Jones and the Kingdom of the Crystal Skull', which made £16.3m in its opening weekend.
Overall cinema audiences were down 7% in January-May and newspaper reports are suggesting that the 7% fall will continue over the whole year with audience figures dropping to 151m in 2008, down from 162m in 2007.
However, Carlton Screen Advertising does not foresee the decline continuing and attributed last May's high figures to the release of 'Spider-Man 3', which came out on the first weekend of May in 2007 and had the third-highest opening weekend of all time.
The wet weather last year also helped to increase cinema admissions, according to Carlton, unlike in May this year, which had lots of sunshine.
Danielle Mather, film and research executive at Carlton Screen Advertising, said: "Admissions will continue to grow this year as there is some really strong film product out.
"July sees the start of a great season of family films including Pixar's 'Wall-E' and Dreamwork's 'Kung-Fu Panda', while 'Hancock' and the long-awaited 'The Dark Knight' [with Heath Ledger] are also released.
"Later in the year however, we are also seeing the return of Bond for 'Quantum of Solace' as well as the sixth instalment of Harry Potter, 'Harry Potter and The Half Blood Prince' and the teen sensation that is 'High School Musical 3'."
'Sex and the City' also began at the end of May but its impact will not be evident until the release of June's admission figures.
The movie version of the long-running TV series made an impressive £8.8m at the box office on the last weekend of May.