Eighteen cases of reactive osteocartilagenous metaplasia of the edentulous mandibular alveolar ridge forming clinical masses that mimic neoplasms are reported. Although most of these lesions appeared histologically benign, three exhibited atypical microscopic features suggestive of chondrosarcoma. Of those cases that were followed, none of the lesions recurred after simple surgical excision. Because many investigators consider all cartilagenous lesions of the jaws potentially malignant, the importance of recognizing this benign condition is stressed.