Osteoblastoma is a rare benign bone tumor and is related to osteoid osteoma with which it has overlapping histologic features. It is sometimes also referred to as Giant Osteoid Osteoma; however, it lacks the characteristic pain of osteoid osteoma and is larger (usually > 1.5 cm). The image shows an osteoblastoma involving proximal tibia in a 15 y/o male. The tumor measured about 2.0 cm in size. It is well-circumscribed and has granular, friable appearance in the center due to calcification. It appears to have destroyed a portion of the cortex. Image copyright: pathorama.ch; used with permission.