Mattie Stepanek, 11, and his mother, Jeni, are shown at their home in Upper Marlboro, Md., Monday, Nov. 5, 2001. Mattie has fought a battle with Muscular Dystrophy most of his life, but has managed to become an accomplished poet along the way. Jeni Stepanek also has the disease, which claimed the lives of three of Mattie's siblings. (AP Photo/ Matt Houston)

Stepanek died at Children's National Medical Center in Washington, D.C., the hospital said. He had been hospitalized since early March for complications related to the disease that impaired most of his body's functions.

In his short life, the tireless Stepanek wrote five volumes of poetry that sold millions of copies. Three of the volumes reached the New York Times' best-seller list.

``Mattie was something special, something very special,'' entertainer Jerry Lewis, who chairs the Muscular Dystrophy Association, said in a statement. ``His example made people want to reach for the best within themselves.''

Stepanek, of Rockville, had dysautonomic mitochondrial myopathy, a genetic disease that impaired his heart rate, breathing, blood pressure and digestion, and caused muscle weakness.

His mother, Jeni, 44, has the adult-onset form of the disease, and his three older siblings died of it in early childhood.

Stepanek began writing poetry at age 3 to cope with the death of a brother. In 2001, a small publisher issued a slim volume of his poems, called ``Heartsongs.'' Within weeks, the book reached the top of the Times' best-seller list, the MDA said.

He wrote four other books: ``Journey Through Heartsongs,'' ``Hope Through Heartsongs,'' ``Celebrate Through Heartsongs'' and ``Loving Through Heartsongs.''

His poems brought him admirers including Oprah Winfrey and former President Carter and made him one of the best-selling poets in recent years.

Stepanek was hospitalized many times over the years. He rolled around his home in a wheelchair he nicknamed ``Slick,'' and relied on a feeding tube, a ventilator and frequent blood transfusions to stay alive.

In the summer of 2001, Stepanek nearly died from uncontrollable bleeding in his throat and spent five months at Children's National. When it seemed he would not survive, the hospital got in touch with a Virginia publisher on his behalf.

Stepanek and his mother had sent the book to dozens of New York publishers, all of whom rejected it, according to Peter Barnes of VSP Publishers. Barnes said he was caught off guard when he read the work.

``I was stunned. Some of it was really good,'' he said Tuesday. ``It was very perceptive and thoughtful.''

VSP Books printed 200 copies of ``Heartsongs'' to be handed out to friends. But after a news conference publicizing the book, interest exploded. ``Heartsongs'' went on to sell more than 500,000 copies.

``Mattie rallied after that,'' Barnes said. ``He went from being on his death bed to becoming this huge publishing success.''

Despite his condition, Stepanek was upbeat, saying he didn't fear death. His work was full of life, a quest for peace, hope and the inner voice he called a ``heartsong.''

``It's our inner beauty, our message, the songs in our hearts,'' he said in an interview with The Associated Press in November 2001. ``My life mission is to spread peace to the world.''

He is survived by his mother.