To date no study has explored persecutory delusions in people who commit sexual offences, and whether attributional style and self-concept are any different between sex offenders with and without persecutory delusions. The present study is preceded by a literature review exploring literature on mentally ill sexually offenders. As this area of research is extremely limited to further understanding of mentally ill sex offenders, literature on individuals with persecutory delusions, specifically attributional style and self-esteem will be presented. Finally, research on attributions and self-esteem in sexual offenders is reviewed. The literature review concludes with implications for future research and clinical interventions. This is followed by a research study that aims to explore the relationship between attributional style and self-concept in men with persecutory delusions who commit sexual offences. Sex offenders with persecutory delusions, sex offenders without delusions and normal controls were compared on implicit and explicit measures of attributional style and self-esteem. The three groups were found to have similar attributional styles and levels of self-esteem and no significant differences were found between the three groups. The results are discussed in light of these findings. Limitations of the study are discussed together with future implications for research and treatment of mentally ill sex offenders.