The author begins explaining the subject of joy in Lacan's theory, after try to distinguish the joy of the Other, the joy phallic and the joy other and discusses its importance at the constitution of the subject. After the author brings a clinical case of risk of autism that was treated in psychoanalysis mother-baby since five months old where the baby loose the early signs of autism, but this clinical case brings still preoccupation because of the prevalence of the joy of the Other in the relationship of the mother with his son.