The aim of this thesis was to explore the symptoms of ASD as reported in children with MPS III. It is presented to the reader as three separate papers. 1) A systematic review of the literature on symptoms of ASD in MPS III, 2) an empirical study investigating the symptoms of ASD in children with MPS III and 3) a critical appraisal and personal reflections of the process involved during the completion of the thesis. Paper One presents a systematic review of the extant literature that identifies symptoms of ASD in individuals with MPS III. 16 articles were identified which met the inclusion criteria. Results identified that symptoms of ASD were present in individuals with MPS III with serious implications for late or misdiagnosis. The literature was largely based on small samples and case studies and there were inconsistencies in the reporting and measurements of symptoms. Recommendations for both clinical practice and future research were made following the results of the review. The empirical study presented in Paper Two sought to identify what symptoms of ASD are present in children with MPS III to improve the knowledge and recognition of such symptoms, given the serious implications for accurate diagnosis and opportunities for intervention. Difficulties with recruitment resulted in a small sample of 17 participants with implications for the testing of planned hypotheses. Despite this, results indicated that parents of children with MPS III report symptoms consistent with a diagnosis of ASD. It was difficult to determine any between group differences given small and unequal subsamples. Methodological strengths and limitations, clinical implications and recommendations for further research were discussed. Paper Three presents a critical appraisal alongside personal reflections of the processes involved during the development and completion of the two papers. It highlights clinical implications of the research and recommendations for future research.