Despite its high prevalence and implications for health care resources, health anxiety is still a relatively neglected area of research. This paper describes the development of the Health Anxiety Questionnaire (HAQ), a measure based on a cognitive-behavioural analysis of health anxiety. The measure was developed to identify individuals with high levels of concern about their health. Psychiatric and medical samples were used in the reported studies. The HAQ was found to have a good internal consistency (coefficient alpha and split-half reliability) and short-term temporal stability (test-retest reliability). Long term stability (one year) was modest but predictably responsive to external events. Analysis of the structure of the HAQ (cluster and factor analyses) revealed four factors: worry and health preoccupation, fear of illness and death, reassurance-seeking behaviour and the extent to which symptoms interfere with a person’s life. Studies of the HAQ’s validity indicate that it has appropriate discriminate validity. It is concluded that the HAQ appears to reflect relatively enduring features consistent with the cognitive-behavioural model of health anxiety. It is anticipated that the HAQ should be able to predict response to reassurance following medical examination.