The question of whether patients should influence medical decisions, and if so how much, is not simple. Among other things, it is necessary to decide whether the patient's well-being should take precedence over respect for the patient's autonomy, or vice versa; whether or not the patient has the capacity to exercise true autonomy; what information should be furnished in order to provide the patient with the basis for making a decision about treatment; and how such information should be provided. This article examines these matters, reviews the pros and cons of various methods for obtaining patients' informed consent, presents some broad guidelines for dealing with informed consent issues in a therapeutic setting, and discusses ethical principles that should be applied in obtaining patients' informed consent to participate in clinical research.