OBJECTIVE The authors assessed the effectiveness of habit reversal training (HRT) to treat a complex motor stereotypy in a healthy 3-year-old female. METHOD This data-based case study involved training parents in HRT to deliver the parent-driven intervention to the child. The frequency of the child's behaviors was estimated daily in 30-min intervals by her parents. RESULTS Outcomes supported the effectiveness of the intervention, with the estimated frequency of the stereotypy decreasing from occurring during approximately 85% of recorded intervals to less than 2% over a period of 4 weeks. Further record keeping over 19 weeks suggested treatment gains were generally maintained over time. CONCLUSIONS The current case study provides preliminary evidence supporting the effectiveness of modified HRT to reduce stereotypies in young children. Further, data suggest that the intervention may be extended to younger ages by teaching parents how to facilitate treatment delivery.