Autism Spectrum Disorder is a neurodevelopmental disorder that affects socio-communicative and behavioral abilities. In the language aspect, there is a greater impairment at the pragmatic level and in non-verbal aspects. The objective of this study was to characterize the severity of Autism Spectrum Disorder in an adolescent, pre-and post-speech-language therapy, and describe the process of speech-language intervention using Picture Exchange Communication System allied to the principles of behavioral analysis applied to language. The Autism Treatment Evaluation Checklist with the parents was applied. Then, a therapeutic program of 14 sessions of 50 minutes was developed, one per week, and then the questionnaire was reapplied. In the course of the therapeutic process, it was possible to observe an increase in the number of figure exchanges independently, an increase in the number of vocalizations with communicative intention or functional speech, longer time of visual contact and social smile, reduction of inappropriate behaviors with a significant improvement in the Autism Treatment Evaluation Checklist score.