This study examined the effects of a two-year maintenance treatment assessed at 1 and 2 years following Parent–child Interaction Therapy (PCIT). Sixty-one of 100 clinic-referred children (M age = 4 years, 4 months) originally diagnosed with oppositional defiant disorder (ODD) completed the standard treatment and were then randomized to PCIT maintenance treatment (MT) or to an assessment-only follow-up condition (AO). Rating scale and observational measures from fathers, mothers, and children were collected before and after standard treatment and at one- and two-year follow-up assessments. Maintenance treatment involved monthly telephone contacts from the original therapist focused on relapse prevention based on principles of PCIT. At the two-year follow-up, MT families showed few changes from post-treatment, as expected. However, the expected decrements for AO control families were not seen. Few differences between MT and AO were found at either follow-up assessment, and there were no significant differences in the rates of change during follow-up. The maintenance of gains among AO families may have resulted from the continuous enhancement of standard treatment or from inadvertent reinforcement for maintenance provided by the assessments of change alone.