As every physician knows, “do no harm” is a basic tenet of medical ethics. Ironically, however, the increasingly powerful science used in patient care may undermine adherence to this tenet. In particular, science now enables the physician to identify “partial patients”—as Greaves defines them—by diagnosing disease or risk factors for disease before physical symptoms occur. But simply by identifying such partial patients, the physician may unwittingly inflict emotional harm on them. “Do no harm” requires the physician to anticipate and minimize such harms.