BACKGROUND: Attention deficit hyperactivity disorder (ADHD) is a common neurodevelopmental disorder that starts in childhood and frequently persists in adults. Electrophysiological studies in children with ADHD provide evidence for abnormal performance monitoring processes and familial association of these processes with ADHD. It is not yet known whether these processes show the same abnormalities and familial effects in adults. METHOD: We investigated event-related potential (ERP) indices of performance monitoring in adults with ADHD compared to age matched control participants. We subsequently investigated whether the ERP indices showed a familial association with ADHD by investigating these processes in first-degree relatives of children with ADHD. This was achieved using an arrow flanker task presented to 21 adults with ADHD, 20 fathers of children with ADHD and 20 control participants. RESULTS: Compared to the control group, both adults with ADHD and fathers of children with ADHD displayed significantly weaker error and conflict monitoring, as indexed by the smaller error negativity (Ne) and the N2 components. These two components were highly correlated within each of the three groups (r=0.53 - 0.65). The groups did not differ on the error positivity (Pe). CONCLUSIONS: These findings closely resemble those previously found in children with ADHD, suggesting that conflict monitoring and early error processing are also abnormal in adults with ADHD; and share familial influences with ADHD throughout the lifespan. The relationship between different indices of performance monitoring may suggest partly common underlying mechanisms or modulators.