In 16 patients who had osteoblastoma treated within the last eight years, the lesions can be classified as vertebral (four cases), central "benign" (seven cases), "aggressive" (three cases) and periosteal (two cases). The radiographic features were highly variable except for the consistent shell of reactive periosteal bone. None of the lesions resembled osteoid osteoma or osteosarcoma. The histological pattern was typical, showing sheets of osteoblasts forming irregular, poorly ossified bone trabeculae in a fibrovascular stroma. The three "aggressive" lesions had a distinctly more ominous histologic pattern, a more destructive radiographic appearance and recurred promptly following local curettage. Treatment varied, but for the vertebral, benign "central," and periosteal osteoblastomas, curettage or marginal resection was generally curative. Local wide resection was required for individual aggressively growing tumors.