This review examines associations between physical activity (PA) and cognitive, behavioral, and physiological outcomes in children with attention-deficit/hyperactivity disorder (ADHD). We reviewed studies on participants ≤18 years old, published in English between January 1998 and December 2014, in PubMed, CINAHL, PsycINFO, and Cochrane Reviews. Twenty-six studies were grouped into two categories: those that did and did not account for effects of ADHD medications. The first category showed lower levels of PA and improved cognitive and behavioral outcomes in youth whose ADHD was treated with medications. The second category showed a positive association between PA levels and cognitive and behavioral outcomes in youth whose ADHD was not treated with medications. For both categories of studies, results were inconclusive regarding physiological outcomes. Randomized controlled trials are needed to better clarify the relationship between PA and outcomes in youth with ADHD, and particularly to understand the impact of ADHD medications on that relationship.