"He hasn't forgotten his roots, and yet he's in the highest position," Poussaint says. "We thought he would just be a wonderful person to exemplify for all the medical students what a doctor can do."

Carson's message for the graduating doctors will likely be about the duty well educated people have in advancing society.

"What are the opportunities that exist to do something with that education in terms of healing society as a whole?" is a question Carson says his speech will address.

One of the problems that Carson might take on in his speech-- which he says will not be "canned" or "jelled" until he gives it--is the increasingly common struggle between health maintenance organizations (HMOs) and doctors.

"Obviously physicians need to be in the forefront of that battle and have to stand up for patients--nobody else is going to," Carson says. "The HMO is not going to do it."

Carson also says he wants insurance premiums to become affordable, and advocates coverage that will encourage people to get preventive check-ups-- such as providing a 1 or 2 percent yearly rebate on healthcare costs.

His extraordinary life and ideas about healthcare are strengthened by a great speaking style, Poussaint says.

"We had him up earlier this year to give a lecture in which he packed the auditorium," Poussaint says. "That was the first time I'd ever heard him speak."

Poussaint was impressed at this first meeting, he says, and the speech likely played a key role in Carson's selection as Class Day speaker for the students who chose him.

"He was a wonderful speaker, he had a gentle sense of humor," Poussaint says.

Procuring the neurosurgery superstar was something of a boon for the medical school. Because he juggles his clinical work with administrative work, still teaches, and gives priority to his family, Carson's calendar is so full that he turns down many speaking engagements simply because his schedule has no opening.

"I love commencements," says Carson. "I used to do 12 a year, now I've cut back to six a year."

But his hectic schedule does not prevent the doctor from taking on what's important, he says, because he makes a point of prioritizing.

"I always say, if you need somebody to do something you have to get somebody who's busy," Carson says. "Because people who are not busy take all day to do nothing."

--Staff writer Lauren R. Dorgan can be reached at dorgan@fas.harvard.edu.