Spondylolysis is a stress fracture of a vertebrae that is a common cause of back pain in teenage athletes. Dean said his back started bothering him when he was running track his junior year of high school. Dean said he decided not to correct the problem because it would require an extensive operation with a long recovery time. But when he got his draft lottery number while an undergraduate at Yale University, he took his X-rays and a letter from his orthopedic surgeon to Fort Hamilton, an Army installation in Brooklyn, N.Y.

Dean said he wanted to find out if he would qualify for officer candidate school if he were drafted. He said he was relieved that the military physical disqualified him from service except in times of national emergency. "I was not anxious to serve in Vietnam," said Dean, whose brother, Charles, died under mysterious circumstances in Laos during the Vietnam War. "I was opposed to the war and I was glad I was classified that way, but it was obviously not my decision."

After graduation, Dean spent some time in Colorado, where he skied despite his back condition. "I do as much as I can do," Dean said. "It was the Army's decision not to take me, not my decision."

Kucinich got a medical deferment for his heart murmer.

Kucinich said in an interview that he opposed the Vietnam War, but would have served if he could. He said as a child he was interested in going to one of the service academies and following in the footsteps of his father, a World War II veteran who had a silver plate in his knee from a combat wound and kept a Marine emblem hanging on the wall. Kucinich has a sister and two brothers who served in the military. His brother Frank served in Vietnam. "The heart murmur changed a lot," he said. "I graduated in '64, a class that took a lot of casualties. ... Sometimes you just have to say but for the grace of God go I."

Lieberman and Gephardt initially had student deferments for undergraduate and law school.

After graduation, Gephardt joined the Missouri Air National Guard as a legal affairs officer and got a 1-D classification that kept him from being sent to Vietnam. Lieberman got a 3-A deferment for becoming a father.

That leaves Al Sharpton--he's the baby of the group. By the time he turned 18 in 1972, the war was just about over, so he never got called.

One more factoid: 25 of the 43 U.S. Presidents served in the military.

Update: See Frank Rich's column in the Sunday New York Times, Why Are We Back in Vietnam?