Public health agencies regularly survey randomly selected anonymous students to track drug use, sexual activities, and other risk behaviors. Students are unidentifiable, but a recent project that included school-level analysis discovered a school with alarmingly prevalent student suicidality. Given confidentiality protocols typical of surveillance, the surveyors were uncertain whether and how to intervene. We searched literature for duties to warn at-risk groups discovered during public health surveillance, but we found no directly applicable guidance or cases. Reasoning by analogy, we conclude that surveyors should contact the school’s leaders to call attention to its outlier status, but public warning is unwarranted. However, such an ad hoc decision to issue a warning, even if only to school leaders, raises significant practical, legal and ethical issues. National public health and education associations should produce guidance that clarifies ethical and legal duties owed to schools and students involved in population health-risk surveillance.