In part because of their core generalist education, physician assistants can change clinical specialties over the course of their work life. This is known as career flexibility. Using medical care providers who can adapt quickly to new opportunities could help alleviate medical workforce shortages in primary care. We studied annual surveys undertaken by the American Academy of Physician Assistants to determine how many physician assistants changed specialties and how frequently. Over four decades, 49 percent of all clinically active physician assistants changed specialties sometime in their careers. This suggests that incentives, such as educational grants, could draw more physician assistants to work in primary care. These findings suggest that an array of new incentives under health reform could draw and retain more physician assistants into primary care medicine.