The presenting duo made the admission when asked by a viewer during an interview on ITV's This Morning.
"Yes, we have played quite a lot of pranks on each other," McPartlin admitted. "We used to go through stages of playing pranks on my wife when we lived in a flat together."
Recalling one in particular, Donnelly continued: "Yeah we did, that was quite cruel actually. The most elaborate one we ever did was when Lisa got up in the middle of the night and went to the loo.
"And then Ant woke me up and got me to replace him in his bed. She came back from the toilet and then he left the bedroom window open, and climbed in through the window…"
"And said, 'What the hell is going on in here?!'" McPartlin added, picking up the story.
The duo were joined by Simon Cowell yesterday as they launched ITV's new gameshow Red or Black?.
> Ant & Dec 'could make £10 million from company sale'
Watch Ant, Dec and Simon Cowell discuss their new show: