Background: Computerised cognitive behavioural therapy provides a unique opportunity to collect and analyse data regarding the idiosyncratic content of people's core beliefs about the self, others and the world. Methods: 'Beating the Blues' users recorded a core belief derived through the downward arrow technique. Core beliefs from 1813 mental health patients were coded into 10 categories. Results: The most common were global self-evaluation, attachment, and competence. Women were more likely,

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... nd men were less likely (than chance), to provide an attachment-related core belief; and men were more likely, and women less likely, to provide a self-competence-related core belief. This may be linked to gender differences in sources of self-esteem. Those who were suffering from anxiety were more likely to provide power-and control-themed core beliefs and less likely to provide attachment core beliefs than chance. Finally, those who had thoughts of suicide in the preceding week reported less competence themed core beliefs and more global self-evaluation (e.g., 'I am useless') core beliefs than chance. Limitations: Concurrent symptom level was not available. The sample was not nationally representative, and featured programme completers only. Conclusions: Men and women may focus on different core beliefs in the context of CBT. Those suffering anxiety may need a therapeutic focus on power and control. A complete rejection of the self (not just within one domain, such as competence) may be linked to thoughts of suicide. Future research should examine how individual differences and symptom severity influence core beliefs.