Background: Social cognitive deficits are considered to be central to the interpersonal problems experienced by individuals with a diagnosis of Asperger syndrome, but existing research evidence regarding mentalising ability and emotion recognition ability is difficult to interpret and inconclusive. Higher levels of mental health problems are experienced in Asperger Syndrome than in the general population, including depression, general anxiety and anxiety-related disorders. Clinical accounts have described symptoms of psychosis in individuals with autism spectrum disorders, including Asperger syndrome, and a number of research studies have reported elevated levels of delusional beliefs in this population. Investigations of social cognition in psychosis have highlighted a number of impairments in abilities such as mentalising and emotion recognition, as well as data-gathering and attribution biases that may be related to delusional beliefs. Similarly, a number of factors, including theory of mind difficulties, self-consciousness and anxiety, have been associated with delusional beliefs in individuals with Asperger syndrome, but there is a lack of agreement in the existing research. A preliminary model of delusional beliefs in Asperger syndrome has previously been proposed, which needs to be tested further and potentially refined. The current study aimed to further investigate social cognitive mechanisms in individuals with Asperger syndrome and to explore potential links with the development of paranoia. Method: Participants with a diagnosis of Asperger syndrome were recruited through a number of voluntary organisations and completed screening measures, the Autism Spectrum Quotient and the Wechsler Abbreviated Scale of Intelligence, to ensure their suitability for the study. Participants in the control group were recruited through the university and local community resources and were matched group-wise with the Asperger syndrome group for age, sex and IQ scores. The study compared the Asperger syndrome group (N=30) with the control group (N= 30) with regard to their performance on four experimental tasks and their responses on a number of self-report questionnaires that were delivered as an online survey. The experimental tasks included two theory of mind measures, one designed to assess mental state decoding ability (The Reading the Mind in the Eyes Test) and one designed to assess mental state reasoning ability (the Hinting Task). The recognition of emotions was evaluated through the Facial Expression Recognition Task. The Beads Task was administered to assess data-gathering style and specifically to test for Jumping to Conclusions biases. The self-report questionnaires were employed to measure levels of depression, general anxiety, social anxiety, self-consciousness and paranoid thoughts. Results: The Asperger syndrome group performed less well than the control group on tasks measuring mental state decoding ability, mental state reasoning ability and the recognition of emotion in facial expressions. Additionally, those with Asperger syndrome tended to make decisions on the basis of less evidence and half of the group demonstrated a Jumping to Conclusions bias. Higher levels of depression, general anxiety, social anxiety and paranoid thoughts were reported in the AS group and levels of depression and general anxiety were found to be associated with levels of paranoid thoughts. Discussion: The results are considered in relation to previous research and revisions are proposed for the existing model of delusional beliefs in Asperger syndrome. A critical analysis of the current study is presented, implications for clinical practice are discussed and suggestions are made for future research.