A belief in the validity of informed consent is one of the most important consequences of the doctrine of autonomy in medical ethics. Truly informed consent requires full disclosure of all relevant information by the doctor, competence of the patient to appreciate what the information signifies, understanding of the facts and issues by the patient, a voluntary choice by the patient and an autonomous authorisation for treatment or entry into a trial. Each of these conditions is hard to fulfil. In particular, full autonomy cannot exist in illness, and this is acknowledged by the act of consultation. The issue is further complicated by the stochastic nature of biological systems and the responses to illness and treatment. Disclosure of likely outcomes is, of necessity, unsatisfactory when a patient seeks surety when entering the clinical process with a serious and life threatening disease. Neither strict logic nor the law provide answers to this problem. The legal and moral issues have become confused. This is unfortunate, because the legal concern often centres on avoidance of actions in law rather than on the more fundamental issue of benefit to the patient. There is a need to teach doctors that discussion is a necessary part of the doctor-patient relationship, that fully informed consent is seldom-if ever-possible, and that skill in understanding what the patient is seeking is more important than the development of rigid and legally "complete" consent forms.