The Washington Post reports the documents show managers of the trusts regularly informed the Tennessee Republican when new shares of HCA Inc. were added to his portfolio.
Frist, who is facing a federal probe of his stock sales, has maintained that he was not aware of what was in the trusts which he once described as "totally blind."
But the Post reports that in the past four years, trustees have written to Frist and the Senate 15 times about transactions in the trusts, including notice of the addition of HCA stock worth at least $500,000 in 2001 and HCA stock worth at least $750,000 in 2002.
According to the trust agreements, the trust managers are required to contact Frist and the Senate when assets are bought or sold.
The Securities and Exchange Commission and the Justice Department are investigating Frist's sale of millions of dollars of stock in HCA, the Nashville-based hospital chain founded by his father and brother. The sales were completed by July 1, two weeks before share prices fell by 9 percent.
In January 2003, Frist told a television interview, "So as far as I know, I own no HCA stock." But two weeks earlier, the Post reports a Frist trustee, M. Kirk Scobey Jr., told the senator in writing that one of his trusts had received HCA stock worth between $15,000 and $50,000.
A Frist spokesman, Bob Stevenson, told the Post, "He (Frist) could have been more exact in his comments," and that Frist might better have said he did not know to what extent he owned HCA stock.
Frist defended his stock sales over the weekend, but said the investigations will affect his decision on whether he will seek the presidency in 2008.
Frist said Saturday during a visit to Iowa — site of the nation's first presidential caucuses — that he has not lost the public's trust and wants people to "wait for the facts before passing judgment."
Before speaking at the Iowa GOP's annual fundraising dinner, Frist told reporters that his visit does not confirm any presidential aspirations. "I've been to Iowa many times," he said.