In the summer of 1910, William James Mayo, M.D., delivered the commencement address at Rush Medical College in Chicago. In his speech, he uttered words that have become the cornerstone of Mayo Clinic's model of care: "The best interest of the patient is the only interest to be considered, and in order that the sick may have the benefit of advancing knowledge, a union of forces is necessary." In this article, we reflect on issues raised by Mayo's speech that strike at the very heart of our professional identity and ask two questions: Is medicine's foremost concern the best interest of the patient? And has medicine really united over the last century in the service of patients?