He made the stinging jibe during a joint press conference held in Washington with Prime Minister Theresa May.
Mr Trump described brexit as a "wonderful thing" and said it hinted at his shock victory in the US presidential election some months later.
He blasted the EU while discussing his attempts to be approved for a development in a European country – presumed to be Ireland, where he owned a development on the west coast but was denied permission to massively expand it.
He said: "I had a very bad experience. I had something when I was in my other world. I have something in another country and getting approval from Europe was very very tough.
"Getting approval from the country was fast, easy and efficient. Getting the approvals from the group, I call them the consortium was very, very tough."
Donald Trump has dismissed the European Union as a
He added: "Brexit was an example of what was to come. I happened to be in Scotland when brexit happened and we had a vast amount of press there. I said Brexit is going to happen. It was scorned in the press for making that prediction."
Donald Trump speaking about the EU this evening
"Low and behold the following day it happened. I think Brexit is going to be a wonderful thing for your country. I think when it irons out you’re going to have your own identity. You’ll be able to make free trade deals without having somebody watching you."
May meets Trump: Historic first meeting in pictures
Fri, January 27, 2017
The two leaders will spend about an hour in face-to-face talks in the Oval Office, where President Trump has restored a bust of Winston Churchill removed by predecessor Barack Obama.
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President Trump Meets With British PM Theresa May At The White House
Both leaders have promised to bring the special relationship between the USA and the UK "even closer" during this historic visit.
This is a developing story. More to follow…