Background: Parent training is one of the most effective treatments for young children with conduct problems. However, not every family benefits from this approach and approximately onethird of children remain in the clinical range at follow-up assessments. Little is known about factors affecting treatment outcome for young children. Method: Hierarchical linear modeling methods were used to examine the effects of child attentional risk factors (inattention, impulsivity and hyperactivity problems), parental and familial risk factors upon the efficacy of a parent training program to decrease boys? conduct problems. Mothers of 81 boys, four to seven years of age, exhibiting conduct problems attended a parent training program (The Incredible Years) which lasted 22 to 24 weeks. Treatment effectiveness was assessed at one month and one year post treatment by means of independent home observations, parent and teacher reports. Results: Results indicated significant decreases in observations of mothers? negative parenting interactions with their children and decreases in their conduct problems according to mother reports and independent observations at home. Boys with elevated ratings of attentional problems in addition to conduct problems showed similar benefits from the parent training program as the boys who did not have attentional problems.