This thesis consists of three chapters, a literature review, an empirical paper and a reflective paper. The literature review explores the relationship between Autism Spectrum Disorder (ASD) and Personality Disorders (PDs). The focus is on examining empirical evidence regarding the shared features as well as the differences between the two types of disorder. The reviewed articles were all cross-sectional studies, with a range of population and comparison sample groups. The review identifies evidence suggesting that ASD and PD presentations share common features as well as displaying some distinct differences. Findings also point to considerable diagnostic co-occurrence of the two types of disorder. Methodological limitations are of the reviewed studies are discussed, clinical implications of the findings are considered and suggestions are made regarding future research directions. The empirical paper investigates the relationship between perceived parenting styles, personality traits and adult attachment style. Data was collected from a non-clinical opportunity sample using a number of self-report measures. Using moderation analysis, explanatory models were created to represent the relationship between perceived parenting, adult attachment style and personality traits. Neuroticism, conscientiousness and agreeableness were the most prominent personality traits, while the relative contribution of these personality traits varied according to gender and adult attachment style. Adult attachment style was also found to be influenced by the perceived type of parenting received from opposite sex parents. The results are discussed in relation to the existing evidence base, as are clinical implications and future research directions. Finally, the reflective paper comprises an overview of personal and professional development whilst undertaking my thesis. This involves a reflective discussion of my attachment style in relation to the research process and how this changed and developed over the course of writing my thesis.