Sinn Fein president Gerry Adams underwent laser surgery for a prostate problem during his trip to New York last August.
According to the Irish Independent, details about the visit have emerged in documents that were filed by Friends of Sinn Fein, a party support group in the U.S.
Adams was kept overnight at the hospital after he underwent the procedure then spent nine days recovering at the apartment of a friend in Manhattan.
Sinn Fein has declined to give specific details about Adams' prostate problem but did go on to confirm that it was "not cancer" and that the treatment he received in New York had been a success.
"Mr Adams was advised that the procedure he required – which involved laser treatment – was best done in New York," the party said in a statement.
Sinn Fein also stated that the cost of the expensive treatment was taken care of by Adams himself.
"Friends of Sinn Fein did not pay any costs toward this treatment nor was there any cost to the Irish taxpayer," it said in a statement.
While in New York, Adams had dinner at Bobby Van's Steakhouse in Manhattan, hosted by the restaurant's president, Joseph Smith. Adams stayed at Mr Smith's home before and after his procedure.
Adams survived a major assassination attempt during The Troubles and has had health problems relating to that in subsequent years.