At the beginning of the article, the author presents basic information on the diagnostic procedure for autism spectrum disorder - main diagnostic criteria currently in force (DSM-5, ICD-10), taking into account the changes occurring in this area, as compared to the DSM-IV criteria, which were applicable until recently. In the second part, she emphasizes how important early diagnostic observation of autistic symptoms is. She analyzes in detail the patterns of normal child development from infancy to early childhood, taking into consideration characteristics that are important from the point of view of the diagnosis of autism: behaviors, emotions, relationships, physical development and communication; she also points to red flags for autism and distinctive early symptoms of autism spectrum disorder at each milestone in the development of infants and toddlers. The author also points out the importance of observing motor development in the child's first year of life in the ASD diagnostic procedure and emphasizes the need to analyze sensory processing difficulties and disorders, which is essential to develop appropriate therapeutic interventions; at the same time, she lists available assessment tools that are, in a way, an introduction to an extended diagnostic process. The third part of the article presents a detailed structure of diagnostic and therapeutic measures, which need to be developed individually for each child by a team of specialists. It also analyzes the special educator's assessment skills and points out threats coming from an inappropriate, unquestioning use of tools to provide functional assessment for children with autism; it also points to such tools that can complement the diagnostic process.