Sleep disturbances (SD) are commonly reported concerns among parents and caregivers of children and adolescents with Attention-Deficit/Hyperactivity Disorder (ADHD). While it is widely acknowledged that SD can worsen various aspects of children and adolescents' well-being (e.g., academic performance and emotional/behavioral state), a comprehensive clinical characterization of ADHD and SD is currently lacking. To address this gap, 136 children and adolescents diagnosed with ADHD (aged 6 to 14 years) were retrospectively selected by reviewing electronic health records of hundreds of patients with neuropsychiatric disorders referred to the children's hospital. Participants were divided into two groups based on the presence of SD, assessed via a parent-report questionnaire (94 ADHD without SD and 42 ADHD with SD). Standardized measures of adaptive behavior, academic performance, ADHD-related and emotional/behavioral symptoms were collected. Results documented that the group of ADHD with SD obtained worse scores in specific aspects of adaptive behavior (conceptual and practical domains), academic performance (text comprehension, writing), ADHD symptoms (inattention) and emotional/behavioral difficulties (especially, mood/emotional regulation and stress) compared to those with ADHD without SD. In addition, our results established a relationship between sleep problems and diverse clinical aspects of children and adolescents with ADHD, while controlling for age, cognitive level, gender, ADHD symptoms severity, and Body Mass Index. From a clinical perspective, our study suggests that the presence of SD in patients with ADHD may serve as an indicator for strengths and weaknesses in this population, even demonstrating an independent relationship with specific clinical dimensions. Implications to improve clinical diagnostic and therapeutic interventions are discussed.