A principal component analysis was carried out on the 62-item Illness Behaviour Questionnaire responses of 832 pain clinics and patients and 746 psychiatric in-patients in the same general hospital. Analyses were carried out for the groups separately, and combined (N = 1578). The factors obtained were compared to those of the original study, Pilowsky and Spence J Psychosom Res 1975, 19: 279-287, and studies by Zonderman et al. Hlth Psychol 1985; 4: 425-436, and Main and Waddell Pain 1987; 28: 13-26. Varying degrees of robustness of the original factors was demonstrated and this is discussed in relation to the clinical context in which the IBQ is used. The significance of five new factors which emerged is discussed. They were labelled 'Interpersonal Sensitivity', 'Responsiveness to Medical Reassurance', 'Illness Impact', 'Self Appraisal' and 'Biological Functions'.