Children with Attention Deficit/Hyperactivity Disorder (ADHD) are at risk for serious adverse developmental outcomes, including criminal behavior, depression, and suicidality. Parenting and parental psychopathology are robust predictors of long-term developmental outcomes in this population. For instance, early maternal positive parenting predicts fewer conduct problems over time among children with ADHD, whereas maternal depression predicts higher levels of future conduct problems. Little is known about biological markers which may be associated with individual differences in maternal parenting in families of children with ADHD. One such biological marker previously associated with parenting in non-ADHD samples is the hypothalamic- pituitary adrenal (HPA) axis and its byproduct, cortisol. Neurobiological models of parenting suggest that cortisol may be associated with variations in parenting such that elevated levels of maternal cortisol following a stressful task are associated with negative parenting in mothers of toddlers with difficult temperaments. Existing studies however, fail to examine the relationship between maternal cortisol reactivity and parenting in school-age children. Additionally, existing studies do not address maternal cortisol reactivity and parenting in mothers of children with ADHD. In non-ADHD samples, difficulty regulating stress responses is related to variations in maternal parenting and poor maternal adjustment, both of which have been found to predict poor developmental outcomes among children with ADHD. Furthermore, mothers' regulation of physiological stress responses may be particularly important for families of children with ADHD, as parenting a child with chronically challenging behaviors represents a persistent environmental stressor. The proposed study seeks to extend the existing literature by providing an empirical examination of the relationship between individual differences in maternal cortisol reactivity following a stressful task and observed parenting behavior in mothers of children with ADHD. This investigation can have implications for understanding biological mechanisms of adaptive maternal parenting among families of children at risk for adverse developmental outcomes.