Anorexia nervosa is a disorder which causes significant impairment, both acute and chronic, for those who experience it. Anorexia nervosa is associated with a long-term course and high rates of relapse. The purpose of this research was to investigate the perspectives of those with anorexia nervosa on aetiology and their views on causes of relapse. The aim was to gain a better understanding of how those with anorexia nervosa conceptualise it; compare it to theoretical models and considered how these perceptions may relate to treatment. Sixteen semi-structured interviews were conducted with eight participants, consisting of eight initial interviews, then eight follow-up interviews to reflect on preliminary findings. Findings related to three main domains: definitions of anorexia nervosa, causes of initial development, and causes of subsequent episodes (relapses). Individual and collective definitions of anorexia nervosa were markedly different from diagnostic definitions, mainly due to the increased detail but there was also contention around how diagnostic definitions focus on body image and resistance to recovery. Causes of anorexia nervosa in this study matched other in-depth research of accounts, but varied with respect to aetiological models. A key difference uncovered in this study was the emphasis placed by participants on different aspects of anorexia, which fell outside of weight and body image concerns, and notable that these aspects became a part of the reasoning for anorexia. Perspectives on the causes of relapse indicated three main categories: those which were present during initial development, those which were present during the initial development but only became significant after experiencing anorexia, and those which were unique to relapse. Due to the limited research in this area it was challenging to compare these findings to other studies; however, they do represent an important aspect of treatment and research, which could be enhanced. A model of aetiology of anorexia nervosa was developed integrating current findings with established theoretical models and research; key influences contributing to relapse were also modelled. Relevant recommendations for diagnosis, treatment, and relapse prevention are presented throughout the discussion.