NASHVILLE - HCA Holdings Inc. said Thursday it will buy back about $1.5 billion of its shares owned by Bank of America Corp., one of the lead underwriters from the hospital operator's initial public offering of stock last March.

The Nashville company plans to repurchase 80.8 million shares for $18.61 each, which was the stock's closing price Wednesday. That represents more than 15 percent of its total shares outstanding. It will buy back the shares using cash on hand and available credit.

The repurchase should be completed by Sept. 21. Three HCA board members designated by the bank - Chris Birosak, James Forbes and Nathan Thorne - then will step down. That will leave HCA with a 12-member board.

HCA is the largest U.S. hospital chain. It owned 164 hospitals and 111 freestanding surgery centers at the end of the second quarter.

It completed a $3.79 billion initial public offering of its stock in March, the company's t hird since it first went public in 1969. A group of group of investors including Bain Capital, Kohlberg Kravis Roberts and Merrill Lynch Global Private Equity had taken HCA private in a 2006 leveraged buyout.

Bank of America, based in Charlotte, N.C., bought Merrill Lynch after that buyout.

HCA shares closed at $31.02 in their first day of trading March, but the stock has slipped since then. Shares rose more than 10 percent, or $1.99, to $20.60 in late morning trading.