We are present a case of duplication of hemi mandible and oral cavity in an adult patient. This is a very rare condition and each and every case warrants publication. This patient is unique in that she would not have presented for surgery if she was married. She presented at 30 years of age. The patient underwent radiological investigations using CAT scan, orthopantogram and routine X-ray films. She was operated on with an elliptical incision around the swelling, excising the whole of the duplicated mandible along with other associated structures such as a salivary gland and the branchial cyst present along with it. Postoperatively the patient had mild marginal mandibular weakness which recovered with time.