Autism Spectrum Disorder (ASD) is a neurodevelopmental disorder associating persistent communication and social interaction deficits with behaviors, interests or activities of a restricted and repetitive nature. The etiology of ASD is not yet fully understood but appears to be multifactorial, including both genetic and environmental factors. The concept of autism underwent a major evolution before arriving at the current definition in DSM-5. The diagnosis has two parts: a categorical from cut-off and differential diagnosis established from a specification of the category by dimensional variables (intelligence, language, associated diseases, adaptation). These two parts (categorical diagnosis and specifiers) are complementary but pose a certain number of practical problems in establishing the diagnosis in adulthood.