The broadcaster’s Q1 trading update released this morning showed its ad revenue was £393m in 2017, down from £433m in the first quarter in 2016.
Total revenue was also down 3% from £755m last year to £731 in 2017.
ITV, which broadcasts shows including Coronation Street, The X Factor and Britain’s Got Talent, expects ad revenue to be down between 8% and 9% over the first half of the year.
It added that April was up 5% and forecasts May to be down 8% and June down 15% to 20% "against the tough comparator" of last summer's Euro 2016 football coverage.
Adam Crozier, ITV’s outgoing chief executive, said: "ITV’s overall performance and the shape of the UK advertising market are very much as we anticipated and our guidance for the full year remains unchanged."
He added: "Online, pay and interactive continued to grow strongly driven by increased demand for online advertising, up 22%.
"ITV Studios total revenues grew 7%, including currency benefit, with a solid pipeline of new and returning programmes coming through.
"Viewing remains strong both on-screen and online. ITV main channel share of viewing is up 4%, ITV Family share of viewing is up 2% and online viewing is up 32%."