Mind wandering seems to be a prototypical feature of attention-deficit/hyperactivity disorder (ADHD). However, an important emerging distinction of mind-wandering types hinges on whether a given episode of mind wandering reflects a failure of executive control (spontaneous mind wandering) or the engagement of controlled processes for internal processing (deliberate mind wandering). Here we distinguish between spontaneous and deliberate mind wandering and test the hypothesis that symptoms of ADHD are associated with the former but not the latter. We assessed ADHD symptomatology and everyday levels of deliberate and spontaneous mind wandering in two large non-clinical samples (Ns = 1,354). In addition, to provide converging evidence, we examined rates of deliberate and spontaneous mind wandering in a clinically diagnosed ADHD sample. Results provide clear evidence that spontaneous, but not deliberate, mind wandering is a central feature of ADHD symptomatology at both the clinical and non-clinical level. We discuss the implications of these results for understanding both ADHD and mind wandering.