Looking at Canadian provincial pediatric health care policies and laws, the best interest standard (BIS) enjoys support. Within philosophy, however, the BIS faces serious opposition. Granted, there remain a few fervent defenders of the BIS in the contemporary literature; however, I argue that while some authors nominally defend the BIS, my analysis reveals that what they really defend is at best a watered down version of it. In this article, I argue that not only must the BIS be understood narrowly, but a substitute decision-maker (SDM) must satisfy the BIS — for an SDM is her patient's fiduciary.