The aim of this study was to analyze motor inhibition and facilitation of adult ADHD patients using double pulse transcranial magnetic stimulation (TMS). Twenty-six right handed adult ADHD patients according to DSM-IV were investigated and compared to 26 age and sex-matched controls. In the left hemisphere, mean motor inhibition was 0.53 +/- 0.33 (mean +/- SD) in ADHD patients and 0.34 +/- 0.16 (mean +/- SD) in controls (p = 0.012). There were no significant differences in motor excitability concerning facilitation or in the right hemisphere. Decreased motor inhibition correlated with a higher symptom score derived from the Wender Reimherr Interview (WRI) (p = 0.28; p = 0.04) and also with self rated hyperactivity/impulsivity symptoms (p = 0.30; p = 0.03). In conclusion, decreased motor inhibition in adult ADHD corroborate similar findings in children with ADHD (Moll et al., 2000) and reflect disturbed impulsivity and hyperactivity on a neurophysiological level.