In this article the author discusses how an evidence-based practice was modified to treat an intellectually disabled client with oppositional behavior. Parent Management Training was modified to treat the client. A single-subject A–B design was used. Behavior improved from 1.57 (SD = .78) to 0.63 (SD = .71) episodes of negative behavior per day from baseline to intervention, and findings were significant (t = 2.83, p = .01). Follow-up with the family indicated sustained improvement one year after the intervention was discontinued. Consideration should be given to using principles of Parent Management Training to create formal plans for addressing problem behaviors across settings with intellectually disabled clients.