Autism spectrum disorders (ASD) are neurodevelopmental disorders at the origin of severe handicap. The clinical expression of these disorders is strongly variable according to the presence of an intellectual deficiency or an associated organic and\or psychiatric disorder. Getting a correct diagnosis of ASD as a child or an adult can help a person and the professionals understand past difficulties, identify his or her strengths, and adapt the right kind of help. A complete diagnosis, realized by a trained multidisciplinary team, allows to define the necessary strategies of global support, in partnership with families. Treatments and services can improve a person's symptoms and ability to function. These characteristics must be regularly assessed in time.