Patients with ADHD display enhanced Default Mode Network (DMN) functioning, resulting in altered functioning with its antagonistic Task Positive Network (TPN). To conduct this systematic review, one investigator performed the search and screening methodology, in which 30 studies were detected that met the criteria. Mixed results were obtained for within DMN connectivity and connectivity between the DMN and TPN. However, majority of studies found reduced anticorrelation between the DMN and TPN, in other words, a reduced DMN suppression. Furthermore, all studies demonstrated that methylphenidate treatment results in a suppression of the DMN. Despite mixed findings regarding DMN intraconnectivity and interconnectivity with the TPN, this systematic review supports the conclusion that ADHD is a disorder of DMN dysfunction including dopamine alterations which can be reversed and treated by methylphenidate. Further research is needed to fully understand the correlation between DMN activity and ADHD.