The primary aim was to explore the factor structure of the Illness Behaviour Questionnaire (IBQ) and the generalisability of the derived dimensions to both general community members and four chronic illness groups. A questionnaire was administered to 675 participants, comprising 344 from the community, 80 with asthma, 95 with diabetes, 79 with chronic pain and 77 with chronic fatigue syndrome (CFS). Illness severity was calculated for all chronic illness participants (self-rated health for community members). Three IBQ scales were derived following an exploratory factor analysis for the whole sample: Affirmation of Illness (α = 0.71 (CFS)-0.79 (asthma, diabetes)), Concern for Health (α = 0.71 (asthma)-0.78 (pain)) and General Affective State (α = 0.70 (CFS)-0.80 (asthma)). Patterns of response across the five samples, and intercorrelations among the new scales and the original seven scales, were largely in accord with expectation. Long-standing criticisms of the IBQ were addressed by using systematic statistical principles to identify meaningful and psychometrically sound IBQ dimensions. The derived structure offers a more parsimonious account of possible illness responses, with the availability of a more concise yet informative index of abnormal illness behaviour having practical utility for researchers and clinicians alike.