Essential hypertension: a sign in search of a disease. The concept of disease is of cardinal importance in medical practice. The current definition has developed over more than 200 years. It includes a distinctive natural history and identifiable cellular changes. Pickering proposed a fundamental alteration to the definition when he suggested that essential hypertension is a quantitative disease without causative cellular change distinguishing normal from abnormal. The nature of essential hypertension has been confused from the beginning because of a category error. Injury is conceptually distinguished from disease. Essential hypertension, defined as elevated blood pressure together with its cardiovascular consequences, is found to be neither an injury nor a disease according to current definitions. Instead, essential hypertension refers to a treatment group just as "the fevers" did in an earlier century. One effect on patients of the failure to resolve this diagnostic paradox is the burden of suffering from the label of "disease" rather than from a state that may be substantially due to their own behavior. A theoretical consequence of importance for psychiatric theory is that the disease status of functional disorders can no longer be defended by an appeal to the existence of a quantitative disease of blood pressure. 