Attention defcit hyperactivity disorder (ADHD) is a neurobiological condition characterized by developmentally inappropriate and impairing patterns of inattention, hyperactivity, and impulsivity [1]. ADHD symptoms usually become more evident in school aged children, are more frequent in boys than girls and tend to persist into adulthood [2]. As for other psychiatric disorders occurring during the developmental age, the categorical and relatively simple symptomatological core of ADHD often does not appear alone. Frequently, a wide variety of concurrent psychiatric disorders contribute to the psychopathological status of children and adolescents with ADHD, with a wellestablished consensus among authors that the presence of overlapping psychiatric disorders is more likely to be the rule than the exception [3]. The medical term commonly used for this concurrence is comorbidity, even though the early meaning of the word as a “distinct additional clinical entity occurring during the clinical course of a patient having an index disease” [۴] is clearly not fully applicable and appropriate to most psychiatric diagnoses. Indeed, the majority of those listed as comorbid conditions represents disorders, multifunctional impairments, and symptom constellations whose clustering together characterizes the clinical condition [5–۷]. The frst study evaluating a broad range of comorbid conditions in children with ADHD was published more than 30 years ago [8], and its main fndings simply highlighted that ADHD is very often associated with other disorders, particularly depression and anxiety disorders, oppositional and conduct problems, and developmental disorders. No considerable evidence followed the study until more than 10 years later, when the emerging understanding of attention defcit disorders and comorbidities was summarized by Brown et coll. in a comprehensive manual [9]. It is now largely agreed that comorbidities are often one of the most important aspects of ADHD [10–۱۵] and this has led, at least for ADHD, to the consideration of their impact on the outcome of the individual child in the longer term [16]. The overall prevalence of psychiatric disorders associated with ADHD in children and adolescents ranges from about 40 to 80% depending on the sample [11, 17–۲۰], with higher rates in clinically referred ADHD children (67–۸۷%) [۳]. Thus, it seems rather clear that, in addition to an ADHD diagnosis, a clinician should consider a whole range of possible psychiatric conditions. The main disorders likely to co-occur with ADHD are: oppositional defant disorder (ODD) (50–۶۰%), conduct disorder (CD) (20–۵۰% in children and 40–۵۰% in adolescents), depression (16–۲۶%) and anxiety (10–۴۰%) disorders, bipolar disorders (11–۷۵%), tic disorders (20%), obsessive compulsive disorders (6–۱۵%), and autism spectrum disorders (65–۸۰%) [۱۱–۱۳, ۱۵, ۲۱–۲۳].