Current national policy in the Republic of Ireland advocates for the inclusion of students with learning difficulties in mainstream schools. With Asperger's syndrome (AS) specifically, it is essential that teachers understand the syndrome and are well versed in appropriate approaches to effectively create an inclusive environment for these students in the mainstream classroom. This paper explores teacher knowledge and understanding of AS while also exploring what affects their confidence in educating students diagnosed with the syndrome. Data collection pre-dated changes to the DSM-V and as such AS is used throughout this paper. A survey was distributed nationally to a random sample of qualified post-primary school teachers. The findings revealed that teachers did not appear to possess an adequate level of knowledge and understanding in relation to the syndrome. Continued professional development programmes in the area appeared to have minimal effect, with those completing programmes scoring only marginally better than those who did not (2.85%). These findings are of concern if these teachers are then expected to foster an inclusive environment, particularly when a high proportion of teachers have previously taught a student diagnosed with the syndrome and their knowledge remains limited.