Recent cognitive behavioural models of obsessive compulsive disorder (OCD) suggest that the misinterpretation of the meaning of intrusive thoughts plays a pivotal role in the escalation of these thoughts to clinical obsessions, but less attention has been paid to why only certain intrusive thoughts become the focus of these misappraisals. Theoretical speculation suggests that thoughts that have relevance for an individual's value system or sense of self may be particularly salient and upsetting for people. The role of thought appraisal and contradiction of valued aspects of self were examined in a nonclinical population. It was hypothesized that participants reporting on upsetting intrusive thoughts would appraise these thoughts negatively and would report that these thoughts contradict important aspects of self to a greater degree than participants reporting on less upsetting intrusive thoughts. Participants (N = 64) were randomly assigned to report on either the most or least upsetting intrusive thought they had experienced. They completed questionnaires on appraisals of these thoughts, valued aspects of self, and contradiction of self. Consistent with predictions, participants reporting on more upsetting thoughts appraised these thoughts in a more negative manner and reported that these thoughts contradicted valued aspects of self to a greater degree than participants in the least upsetting thought group. These results support Salkovskis' (1985) and Rachman's (1997, 1998) cognitive behavioural models of OCD, and suggest that the degree of contradiction of self may help us understand why some obsessional thoughts are much more upsetting than others.