Collusion is a mostly unconscious phenomenon occurring in the therapeutic relationship, which can be commonly identified in psychiatry but more generally in medicine. Collusion is especially present in circumstances in which the effects of disease and its treatments have a heavy impact on patients and caregivers, and where the stakes are existential. Collusion is triggered by unresolved psychological problems, for example, loss, intimacy or control, which are shared by the patient and the clinician. Collusion, if unrecognized, can seriously hamper the clinician-patient relationship and the care of the patient.