The best interest standard is the threshold most frequently employed by physicians and ethics consultants in challenging a parent’s refusal to provide consent for a child’s medical care. In this article, I will argue that the best interest standard has evolved to serve two different functions, and that these functions differ sufficiently that they require separate standards. While the best interest standard is appropriate for choosing among alternative treatment options for children, making recommendations to parents, and making decisions on behalf of a child when the legal decision makers are either unable to make a decision or are in dispute, a different standard is required for deciding when to seek state interference with parental decision-making authority. I will suggest that the harm principle provides a more appropriate threshold for determining when to seek state intervention than the best interest standard.