This study investigates the role of an emerging legal doctrine, the precautionary principle, in the development of the plan to manage West Nile Virus in the City of Toronto during the 2003 season. Specifically, it asks whether the precautionary principle, widely expected to transform environmental and public health decision-making, operated as a map or guide to officials trying to navigate through the uncertainty associated with both the virus and the “cure.” Although the study focuses on a very particular local context, it also addresses the broader challenges that are gathering for governments hoping to lean on the precautionary principle for policy guidance in the face of controversy. In the case of West Nile Virus, public health officials seemed to confront an intractable problem: taking precaution with respect to the virus, an uncertain public health hazard, meant facing the uncertain environmental and health risks associated with chemical pesticides. The study draws on qualitative empirical data gathered from participant observation sessions in the Toronto city council chamber and comprehensive semi-structured interviews with almost a dozen key policy actors. The purpose of this detailed empirical analysis is to evaluate the potential of the precautionary principle as a policy instrument in light of a common claim of the principle's critics. Can it point the way out of controversy? Or does the precautionary principle, as is argued by legal academics such as Cass Sunstein, “point in no direction at all”?