Background: This study explores the emotional challenges faced by staff working on a sex offender treatment programme for people with an intellectual disability. Methods: Semi-structured interviews were carried out with eight participants working on a treatment programme for sex offenders with an intellectual disability. Interviews were analysed using interpretative phenomenological analysis. Results: Staff experienced a range of negative emotions that they dealt with in a variety of ways including through the use of humour and various emotional defences. Empathy was a challenging and complex issue with individuals taking a variety of positions. Conclusion: Staff awareness and understanding of the role of emotions in relation to their own well-being and in relation to therapeutic processes varied. Emotional intelligence was associated with greater therapeutic understanding. Recommendations are made in relation to personal and professional characteristics and need for clinical supervision to support staff well-being and the development of therapeutic competence and effectiveness.