Trump tweeted that Kudlow is in Walter Reed Medical Center, a military hospital in suburban Maryland. White House Spokeswoman Sarah Sanders told reporters later that Kudlow was in good condition.
Kudlow, born in 1947, was appointed by the president in March to replace Gary Cohn as director of the National Economic Council.
Kudlow, a longtime television commentator, has been a staunch defender of Trump's much-criticized stance on global trade.
Kudlow has just returned from a visit with Trump to the Group of Seven summit in Canada, where trade tensions further divided members of the rich-country club.