This paper explores the balance between common good and individual liberty in the context of public health regulation. The issues are explored in reference to two areas of regulation, isolation and quarantine in the case of SARS, and the rights of parents to refuse mandatory childhood immunizations. In the case of SARS, the analysis explores the age old practice of isolation and quarantine, an important preventive measure with clear civil liberty implications. In reference to childhood immunization the paper considers the American controversy involving the refusal of parents to have their children vaccinated, fearing that mercury in vaccines will lead to autism. The analysis explores the US Supreme Court case of Jacobson v. Massachusetts which 100 years ago established a four part test for evaluating claims of individuals that government public health authorities were infringing on their liberty interests. The paper endorses the four elements of necessity, reasonableness, proportionality, and harm avoidance identified in Jacobson, but calls for a more rigorous scientific evaluation to accompany this traditional test.