The aims of this study were to examine the construct validity of a cognitive behavioural treatment model for medically unexplained physical symptoms and to examine potential predictors of treatment outcome. In concordance with the treatment model we used, the extent of hypochondriacal cognitions and psychological distress at baseline appeared to be associated. Change in hypochondriacal cognitions was related to change in psychological distress. The extent of hypochondriacal cognitions after treatment was predictive of the level of psychological distress at one year follow-up. The only baseline variable that predicted a negative treatment outcome was illness behaviour.