Pervasive Developmental Disorders (PPD) refers to the group of disorders characterised by delayed or inappropriate development of multiple basic functions including socialisation, communication, behaviour and cognitive functioning. The term autistic spectrum disorders was established as a result of the magnitude of the intensity of symptoms and their proportions observed in all types of pervasive developmental disorders. Asperger's Syndrome (AS) remains the most controversial diagnosis in terms of its place within autism spectrum disorders. AS if often described as an equivalent of High Functioning Autism (HFA) or as a separate spectrum-related disorder with unique diagnostic criteria. Another important issue is the relationship between AS and speech disorders. Although it is relatively easy to draw a line between children with classical autism and speech disorders, the clear cut frontiers between them still remain to be found. The main distinguishing feature is the lack of stereotypic interests and unimpaired social interaction observed in children with speech disorders, such as semantic-pragmatic disorder.