The Health Care Consent Act, 1996, states that every person in Ontario, regardless of age, is presumed to be capable of consenting to or refusing medical treatment unless he or she is found incapable with respect to a specific treatment or plan of treatment. Health care practitioners may find it especially challenging to apply the legal test of capacity to young people. As an aid to assessment, a guide incorporating both legal and medical perspectives has been developed. This article describes the background and context of the development of the guide and explains how it helps practitioners to conduct a simpler, more focused evaluation of capacity in youth. The guide, along with an introduction and comments for parents, is included in an appendix.