What renders some mentally disordered patients incapable of informed consent to medical interventions? It is argued that a patient is incapable of giving informed consent owing to mental disorder, if a mental disorder prevents a patient from understanding what s/he consents to; if a mental disorder prevents a patient from choosing decisively; if a mental disorder prevents a patient from communicating his/her consent; or if a mental disorder prevents a patient from accepting the need for a medical intervention. This paper (...) holds that a patient's capacity to give informed consent should be assessed clinically by using these conditions necessary for informed consent, and should be assessed specifically for each intervention and specifically at the time when the consent has to be given. The paper considers patients' incapacity to give informed consent to treatment, to give informed consent to be examined clinically, and to give informed consent to participate in research. (shrink)