OSTEOMA has been defined as a benign, slow-growing, encapsulated bony tumor attached to, or incorporated in, the bone from which it arises. From an academic point of view this definition may be fairly adequate, since osteoma does not metastasize, seldom recurs after removal and presents a microscopic picture characteristic of a benign growth. Yet from the clinical standpoint it is rather incomplete. As will be pointed out later in the discussion, this type of neoplasm may have either a slow or a relatively fast rate of growth, depending on the phase of bone development in which it appears. Then, again, though histologically benign, this tumor may become clinically malignant by virtue of being located in the proximity of many important structures. The consensus of all those who have made a study of this subject is that osteoma of the nasal accessory sinuses is not a common condition and that it