The statement vaguely described the procedure as "an embolization procedure to treat a benign kidney condition" but offered no additional details about the first lady's condition or treatment.
Trump is the first U.S. First Lady to undergo a serious medical procedure while in the White House since Nancy Reagan underwent a mastectomy in 1987, CNN reported.
The president made another unannounced trip just after 4:00 p.m. on Tuesday to visit his wife.
"I want to start by saying that Melania is in the hospital doing really well".
Trump is speaking at the 37th annual National Peace Officers' Memorial Service in Washington.
Target Allegri insists he's sticking with Juventus
The trophy will be awarded then and a farewell ceremony expected to honour retiring skipper Gianluigi Buffon. Juventus won the Serie A title for a seventh straight season on Sunday following a 0-0 draw at Roma .
At the Capitol later, where he joined Republican senators at their weekly lunch, Trump reiterated that his wife is "really doing well". Mrs. Trump also represented the administration at the April funeral of former first lady Barbara Bush.
The 48-year-old first lady had an "embolization" procedure Monday at a military hospital outside Washington. The US president turns 72 next month. "Will be leaving hospital in 2 or 3 days", Trump tweeted.
On Monday, the White House released a statement informing the operation to be successful.
Ms Trump's spokeswoman had said on Monday that the first lady was likely to remain in hospital for "the duration of the week".
Two urologists who have no personal knowledge of Trump's condition said the most likely explanation for the embolisation procedure is a type of noncancerous kidney tumour called an angiomyolipoma. "Embolization can be used to stop bleeding, as in cases of trauma, or to starve a fibroid or tumor of its blood supply, as may be the case in the treatment performed on Mrs. Trump".