Attention Deficit/Hyperactivity Disorder (ADHD) is a prevalent and debilitating disorder diagnosed based on persistent and developmentally inappropriate levels of overactivity, inattention and impulsivity (Tripp & Wickens, 2009). Based on DSM-5, ADHD is divided into three types: ADHD Type1 (Inattention), ADHD Type2 (Hyperactive/Impulsive) and ADHD Type3 (Combined). Neuroimaging studies have identified altered connections between different brain regions in patients with ADHD compared to healthy controls. In this study, we extensively examined whole-brain functional connectivity impairments in ADHD. In addition, we also examined whether the brain’s connector hubs, specialized regions with connections to multiple brain networks and considered critical for the brain’s integrative functions, are involved in this disorder. We used a network metric called functional connectivity overlap ratio (FCOR) estimated from resting state functional MRI to examine connectivity alterations across several large-scale functional brain networks in patients with ADHD compared to healthy controls or patients with ADHD Type1 compared to patients with ADHD Type3. Data from ADHD-200 were used in the analysis. MRI data from patients with ADHD (N = 188) and age- and sex-matched health controls (N = 322) were extracted. The results revealed widespread connectivity alterations of several large-scale functional brain networks in ADHD patients. Specifically, the core neurocognitive networks (salience, default mode, and executive control) showed connectivity alterations across widespread brain regions in the patient group compared to control group. Connector hub regions located primarily in middle frontal gyrus and medial postcentral gyrus also showed significantly higher connections with multiple brain networks in the patient group as well as connector hubs located in the insula and medial postcentral gyrus differentiating ADHD subtypes. Taken together, these findings highlight the involvement of connector hub regions in the pathophysiology of ADHD. Their impairment affects the normal functions of multiple networks and potentially leads to the different clinical manifestations observed in this disorder.