As Jack worked hard to get his name into the limelight, his medical condition became worse each day. He needed the use of crutches when he walked from his Senate office to the chambers. In the late spring of 1954, Jack's back pain became worse than at any other time. He returned to the Lahey Clinic in August where X-rays revealed that his fifth lumbar vertebra had buckled under pressure. The only remedy was a dangerous surgery that could leave him paralyzed if it was not successful. His Addison's disease was an additional complication; it left him more prone to infection.

Jack was determined to undergo the surgery despite the risks. He told his father that he would rather be dead than remain in pain and on crutches. Joe Kennedy and his doctors, though, were hesitant to proceed immediately. On October 10, 1954, Jack arrived at the New York Hospital for Special Surgery ready for his operation. Surgeons determined that they would try a special treatment first. On October 21, after the surgery had been postponed three times, Jack finally underwent a three-hour operation in which a metal plate was inserted in his spine.

Jack emerged from the surgery in stable condition, but within three days he developed a urinary tract infection. Antibiotics were ineffective, and Jack's condition deteriorated. He fell into a coma. When the doctors told Joe Kennedy that Jack was expected to die within hours, a distraught Joe called a priest to deliver last rites. Amazingly, just days later, Jack triumphed over his condition.

By December, his recovery was so slow that his doctor recommended that he move into the family's Palm Beach home. Progress was still slow two months later. Jack was in pain and still unable to walk. It was determined that he had an infection and would need an operation to remove the plate. It was removed on February 15, 1955. Jack recovered within three months and returned to the Senate to a warm welcome by his colleagues. His surgery had failed to escape the watchful eye of reporters, but Jack caught a lucky break. It was reported that his condition was a result of the injuries he had suffered during his service in the war.