This thesis comprises three chapters exploring health professionals’ experiences and attitudes regarding diagnoses that challenge mental health services. The first chapter is a systematic literature review investigating the impact of training on staff attitudes towards personality disorder. Eleven articles were reviewed and critically evaluated. Despite inconsistencies in the data and a number of methodological concerns, there is evidence to suggest that training is effective in improving staff members’ cognitive and affective attitudes towards personality disorder, and their therapeutic engagement with service users. Clinical and research implications are discussed in relation to developing staff training packages regarding personality disorder. The second chapter is a qualitative study of mental health nurses’ experiences of caring for adults with autism spectrum disorder (ASD) in acute inpatient services. Semi-structured interviews were conducted with seven nurses and the transcripts were analysed using Interpretative Phenomenological Analysis. The two major themes that emerged from the data indicated that nurses felt confused and unable to make sense of autistic presentations, but were able to overcome these challenges by focusing on their core nursing values and providing person-centred care. Overall, the findings highlight mental health nurses’ lack of knowledge about ASD. Clinical implications are discussed in relation to developing staff members’ skills and confidence in working with this client group. In the third chapter, personal reflections on the research process are discussed, with a particular focus on stigma and stereotyping in mental health services. These include the evolution of my own perspective and a consideration of the role of clinical psychologists in supporting staff.