Attention Deficit/Hyperactivity Disorder (ADHD) is associated with deficient motor and cognitive inhibitory mechanisms. The aim of this article is to examine two symptoms associated with cognitive disinhibition, namely: intrusive unwanted thoughts, worrisome thoughts and their suppression. Thirty-seven college students diagnosed with ADHD and 23 healthy college students were compared on the Distressing Thoughts Questionnaire and on the Anxious Thoughts Inventory. Results show that in comparison to the control group, participants with ADHD experienced significantly higher ratings on all intrusive thoughts scales, and three worrisome thoughts scales. Our results suggest that worrisome intrusive thoughts are an important phenotypical expression of adults with ADHD. A neurobiological explanation for this phenomenon is suggested, and clinical implications are discussed.