Regression is often seen in the early development of children with autism. The causes of regression, its relationship with the regression found in other pervasive developmental disorders, specific therapies and above all its meaning within the context of the autistic disorder have not yet been fully understood. Its incidence within the autistic population has been found to be between 20% and 49%. The aim of this study is to identify the children who presented regression (or set back or speech-loss) within a sample of 40 children with autism. The characteristics of this group with regression have been analysed in terms of frequency, age of onset, presence of triggers or other contributing factors and the areas of effected development. Moreover the relationship and the differences between children with autism who presented a regression and those who did not have been studied by using a series of variables.