When discussing the optimal scope of the duty to protect patients’ privacy, the literature compares two incommensurable interests: privacy and safety. Policymakers face a difficult task when trying to find an optimal solution, balancing these two, often conflicting, interests. In this article, we confront the trade-off between patient confidentiality and public safety as manifested in the legal duty to warn or report potentially harmful patient behavior. The incommensurability problem seems to plague the analysis of the two interests: what comparable rudiment do privacy and public safety share in the duty to warn or report context? We develop a model which solves this problem by finding the optimal balance between protecting patient’s privacy (as a means to encourage patients to seek treatment, thus reducing risk in society) and warning third parties or the state (again as a means to reduce risk in society). Our model shows that imposing an unqualified duty to report or warn might result in an increase in the dangerousness of the primary behavior society is concerned about, such as piloting, driving or violent acts. Developing a formula not much more complicated than the Hand formula, we show how the chilling effect and the effectiveness of the medical treatment must be factors that courts should consider when imposing a duty on medical professionals to report their patients to the state or enforcing a duty to warn third parties.