Evidence-based practice in psychotherapy carries widely unacknowledged consequences for ethical clinical practice. Informed consent to psychological treatments is an ethical imperative in clinical practice, and there is an ethical obligation for psychiatrists, psychotherapists, and clinical psychologists to provide adequate disclosure to patients about treatments. This is codified within the professional guidelines of the American Psychological Association (APA) and the American Medical Association. Given the APA’s commitment to evidence-based practice, the objective of this paper is to argue that the provision of information about how treatments work should be based on evidence-based research on psychotherapeutic treatments. Case-based scenarios are used to illustrate a range of ethical issues pertaining to evidence-based practice and informed consent in psychotherapy. This paper argues that informed consent processes in psychotherapy must be commensurate with the latest integrated findings on empirically—supported treatments; process research into psychological treatments; research into therapist expertise; as well as evidence about individual patients’ characteristics, culture, and preferences. Our conclusions for practice are challenging: standard ethical interpretations of informed consent to psychotherapy must go further. It is not sufficient for therapists only to describe the specific techniques associated with particular treatment modalities, it is also necessary to disclose information about nonspecific factors. There appears to be consensus among therapists and psychotherapy researchers that these factors are relevant to successful treatment outcome. Our paper aims to launch fresh, serious, pragmatic debate in professional psychotherapy about necessary revisions of ethical codes with respect to information disclosure.