Attention Deficit/Hyperactivity Disorder (ADHD) is associated with action control problems such as failure to inhibit inappropriate responses. Two studies investigated whether self-regulation by implementation intentions (if-then plans; Gollwitzer, P. M. (1999). Implementation intentions: Strong effects of simple plans. American Psychologist, 54, 493–503) facilitates response inhibition in children with ADHD. In Study 1, children with ADHD who furnished a suppression goal with implementation intentions improved inhibition of an unwanted response on a Go/NoGo task to the same level observed in children without ADHD. Study 2 showed that a combination of implementation intentions and psychostimulant medication resulted in the highest level of suppression performance in children with ADHD. Theoretical and applied implications of these results are discussed.