Osteoblastoma, a bone-forming neoplasm without metastatic potential, can be mistaken histologically for various benign and malignant primary neoplasms of bone or mimic nonneoplastic conditions, including osteoid osteoma, giant cell tumor of bone, aneurysmal bone cyst, and chondroblastoma . The most important diagnostic distinction is to distinguish osteoblastoma from osteosarcoma. Although both lesions usually have characteristic clinical, radiologic, and histologic findings, in certain cases the distinction between both can be difficult. This is complicated by lesions that morphologically and biologically appear to exist at the interface between the two. In this review, we describe the characteristics of osteoblastomas and review criteria that can prove helpful in the distinction among the various pathologic entities.