Merlin Entertainments said like-for-like revenue growth slipped to 0.3% in the third quarter after terror attacks and wet weather kept customers away from its theme-park attractions.
Total revenue grew 12.4%, boosted by favourable currency movements and the opening of new facilities abroad, such as Legoland Japan.
Merlin said trading in recent weeks has remained "mixed". It forecast like-for-like revenue growth for 2017 to be flat on 2016.
"Reflecting this, and careful management of the cost base, 2017 EBITDA is expected to be in the range of £470 to £480 million," the company said.
As for the 2018 financial year, the company was similarly cautious.
"Whilst it is too early to predict the outlook for 2018, it is likely that the recent trends experienced in London will persist for the foreseeable future," it said.