Previous literature suggests that children with attention-deficit/hyperactivity disorder (ADHD) exhibit a positive bias (PB), defined as an over-estimation of one's own ability as compared with actual ability. However, it is possible that the larger discrepancy (i.e., PB) in children with ADHD is accounted for by lower competence levels rather than unusually high perceptions of competence. In this study, we investigated the extent to which PB is a perceptual bias associated with ADHD and/or a function of low competence. Thirty-two children who met research diagnostic criteria for ADHD and 31 control children were exposed to a novel task where possible success on the task (i.e., competence) was manipulated. This procedure created low, medium, and high levels of competence in children with and without ADHD, and PB was measured at each level of competence. Six, 2 (ADHD or no ADHD) × 3 (competence levels: low, medium, or high) mixed-model analyses of variance (ANOVAs) were conducted with children's estimation of their competence and PB. The results indicated that ADHD status was not significant, whereas competence level was significant in five out of six analyses. Implications for the measurement and conceptualization of PB in ADHD are discussed.