A significant body of longitudinal research suggests increased rates of mood disorders as well as depressive symptoms in youth diagnosed with attention deficit/ hyperactivity disorder (ADHD) in contrast to non-ADHD comparison youth. Furthermore, individuals with co-occurring ADHD and mood disorders experience more serious impairments and worse outcomes than those with either disorder alone. However, few studies have examined the underlying mechanisms which may better elucidate the relationship between ADHD and depression in youth. The present study examined emotion regulation as a mediator in the relationship between ADHD and depressive symptoms in youth. Moreover, effortful control was examined as a mediator in the relationship between ADHD and emotion regulation. Participants included 69 youth between the ages of 10 and 14 with (n = 37) and without (n = 32) DSM-IV ADHD. Parent and youth ratings of depressive symptoms and emotion regulation were collected, and youth completed computerized measures of effortful control. Results demonstrated significant differences between youth with and without ADHD on depressive symptoms and emotion regulation ability, but not effortful

control. Furthermore, emotion regulation fully mediated the relationship between ADHD and depressive symptoms. Clinical implications and limitations are discussed.