The major objective of this study is to evaluate the effectiveness and generalization of Parent-Child Interaction Therapy (PCIT) for the treatment of 3-6 year old children with Oppositional Defiant Disorder. One hundred preschool children referred for treatment of conduct problem behaviors during 2 years who meet study criteria will be randomly assigned to a PCIT group or a Wait-List control group, with 34 children in each group estimated to complete treatment. Outcome results at 4 months post-intake will be compared between children treated with PCIT, Wait-List control children, and treatment drop-outs. Outcome results at 8 months post-intake will be compared between children who completed PCIT and PCIT drop-outs. Treatment outcome measures include: parent-child interaction observations of parent and child behaviors; parent ratings of family stress, marital satisfaction, depression, and child problem behaviors; teacher ratings of child behavior; and school observations. In addition to examining treatment outcome variables, this study will examine differences between treatment completers and treatment drop-outs on demographic and family functioning variables assessed at pre-treatment. Within the drop-out group and within the treatment completer group, the relationships between length of time in treatment and severity of presenting problems, parental characteristics, and treatment outcome variables will be assessed. Finally, data collected on treatment subjects in the school will be compared to randomly selected classroom control children within the classrooms of the treatment subjects to further assess the clinical significance of changes in school behavior.