The physician who cares for adolescents should routinely assess the medical decision-making capacity of the minor. The physician must always ask whether the young person has the capacity of discernment, after having given the patient the necessary information, and before obtaining his consent. This analysis is helpful for the physician to determine who can make the decision, and to consider the limits of confidentiality. This paper reviews the Swiss law situation in terms of age limits, and provides information to guide the physician in the evaluation process with the use of practical questions and help of other professionals when in doubt.