Attention-deficit hyperactivity disorder (ADHD) is the most prevalent neurodevelopmental disorder in children and adolescents, and it is frequently associated with a range of comorbidities. However, an analysis of critical factors -such as mortality, legal issues, access to care, and academic or occupational impairment- reveals that the most serious comorbidities of ADHD are primarily psychiatric in nature. These include depression, suicidal behaviors, substance use disorders, legal problems, and personality disorders, particularly borderline and antisocial personalities. These comorbid conditions share core features, including difficulties with self-regulation, impulsivity and repetitive behaviors. They also exhibit overlapping neurological and genetic substrates, as well as common environmental risk factors. A review of the current literature underscores the significant morbidity and adverse outcomes associated with ADHD when these comorbidities are present. Given the complexity and severity of these conditions, it is crucial for clinicians working with children and adolescents, to be vigilant about monitoring their appearance. Early recognition and intervention may help mitigate the risk of developing these associated psychiatric disorders and their long-term consequences. Furthermore, evidence suggests that timely and appropriate treatment of ADHD can play a protective role in preventing the onset of these comorbid conditions.