The authors present a rare case of anaplastic alveolar rhabdomyosarcoma (ARMS) occurring after Mandibular Distraction Osteogenesis. A 16-month-old male presented with a rapidly enlarging left lower jaw mass after removal of mandibular distractors placed shortly after birth for Pierre Robin Sequence and severe obstructive sleep apnea. Incisional biopsy of the mass revealed ARMS with anaplastic features. Although ARMS is an extremely rare entity, craniofacial surgeons should have a low threshold for seeking further diagnostic modalities of a growing mass postmandibular distraction.