With surprising frequency, and to the considerable dismay of health care professionals, patients both subtly and overtly refuse to cooperate with medical treatment. Despite considerable empirical and theoretical attention, and an abundance of interventions designed to combat it, noncompliance continues. Its persistence is accompanied by considerable costs borne by patients and society alike. The theory of psychological reactance sheds new light on the phenomenon. Reactance theory proposes that a perceived threat to an individual' freedom generates a motivational state aimed at recapturing the affected freedom and preventing the loss of others. In a medical context, patients' perceptions of threats to their freedom or control may induce noncompliance. This theory permits integration of many of the seemingly disparate and/or contradictory findings, and may afford professionals new opportunities for improving patient compliance.