Objective: Negative priming (NP) is the slowed response to a stimulus that was previously ignored. Response times in NP task conditions were compared with the interference provided by congruent/incongruent stimuli in a Stroop condition in the same task in children diagnosed with attention-deficit hyperactivity disorder (ADHD), their unaffected siblings, and independent controls. Method: Speed, accuracy, and variability of responses were compared using a computerized NP Stroop test for 35 children with ADHD, 24 siblings without diagnosis, and 37 independent healthy controls aged 6 to 17 years. Results: NP was evident at test onset for congruent trials in children without a diagnosis and was reduced initially in those with ADHD occurring in the absence of a significant Stroop interference effect and independently of age or symptom severity. Incongruency masked NP effects. Cases showed more intraindividual response-time variability. Conclusions: Both NP in normal children and its reduction in ADHD cases attenuated across trials reflecting the increased facilitation from previous stimulation. (Contains 4 tables.)