This article aims to discuss the issue of coexistence of the ADHD and PTSD diagnoses in children and adolescents. The literature review presented in the article describes how early chronic stress experiences activate the long-term stress response. Children who have experienced early life trauma, may in their childhood, adolescence and often in adulthood, have to cope with the feelings of overwhelming anger, fear, aggression, agitation and dissociative states. These cognitive and emotional disruptions that occur in response to trauma may overlap with ADHD symptomology. From an epidemiological perspective, trauma exposure and ADHD are pervasive in childhood, what in some situations, may lead to difficulties in making a correct diagnosis. The article discusses the symptomatology similarities as it may give important clinical implications to identify and treat these problems. The author presents the model of psychotherapy based on psychoanalysis and P. Fonagy's theory of mentalization and the review of researches estimating the effectiveness of this approach. The short case study illustrates the research and theoretical material.