A 12-year-old female was referred from a dental clinic due to a radiolucent area under the lower right first and second premolars. The lesion was diagnosed as a simple bone cyst radiographically. However, she complained lasting pain during 10 month follow up. Therefore curettage was performed and it defined as an osteoid osteoma on the histopathologic examination. As the lesion recurred, one year later, enucleation was performed. We report this case to help the diagnosis of osteoid osteoma in mandible.