We present a system for 3D planning and pre-operative rehearsal of mandibular distraction osteogenesis procedures. We describe two primary architectural components: a planning system that allows geometric bone manipulation to rapidly explore various modifications and configurations, and a visuohaptic simulator that allows both general-purpose training and preoperative, patient-specific procedure rehearsal. We provide relevant clinical background, then we describe the underlying simulation algorithms and their application to craniofacial procedures.