Autism spectrum disorder (ASD) is a lifelong condition characterised by persistent deficits in social communication and social interaction, and restrictive repetitive pattern of interests or behaviours. There is abundance of research investigating ASD in children but there is little emphasis placed on its evolution in adult life in terms of clinical features and co-morbidity. Recent studies done on adults suggest that some reduction in number and severity of ASD symptoms during adulthood can be expected particularly in those without mental retardation. However studies also report high levels of psychiatric comorbidity and dysfunction comparable to adults without ASD. It has been highlighted that psychiatric symptoms might be masked by autistic features or autistic features can be mislabelled as a separate psychiatric illness. This might lead to inadequate identification and assessment of adults with autism as well as inadequate recognition and treatment of coexisting mental health problems. A better understanding of developmental changes in autistic symptomatology and their relation to comorbid psychopathology would have important implications.