This study compared attributions for child behavior among mothers of 38 nonproblem boys, 26 boys with attention deficit hyperactivity disorder (ADHD), and 25 boys with ADHD and oppositional defiant (OD) behavior. Boys ranged from 7 to 10 years of age. To capture different aspects of mothers' attributions, 2 assessment methods were employed: (a) ratings of the internality, controllability, globality, and stability of causes for written descriptions of child behavior and (b) coding of the types of causal attributions that mothers provided in vivo while watching their own child's behavior. In response to the written descriptions of child behavior, mothers of boys with ADHD/OD rated the causes of oppositional and inattentive-impulsive child behaviors as more stable and global than did mothers of nonproblem boys. In identifying causes of their own child's failure on lab tasks, mothers of boys with ADHD/OD provided more child-negative attributional causes than did mothers of either ADHD only or nonproblem boys. Implications for assessing and understanding attributions in families of children with ADHD and OD are discussed.