Adenomatoid odontogenic tumour (AOT) is an uncommon , hamartomatous ,benign epithelial lesion of odontogenic origin(3%) that was first described by the driebaldt in 1907 as pseudo–adenoameloblastoma . Here we report a case of adenomatoid odontogenic tumour (AOT)in the mandible in a young girl of 16yrs old and its surgical management and importance of excisional biopsy , which is a gold standard for diagnosis , and its use in planning of treatment with no recurrence during the follow–up has been discussed .