Frontal sinus osteomas, whether cortical or cancellous by morphologic radiologic appearance, appear to represent metaplasia rather than neoplasia occurring at the frontal-ethmoid suture line. These osteomas are not infrequently found completely or partially within the frontal sinus or adjacent ethmoid complex. Regardless of specific anatomic site, they occur at the embryologic junction of enchondral and membranous frontal bone. Those osteomas which produce mechanical complications (ostial obstruction or facial deformity or proptosis) give clear indication for surgical intervention. A much larger group of osteomas, however, is detected on routine plan radiographic examinations carried out for other reasons. Unfortunately, the singular conventional radiographic finding of an osteoma has, in the past, frequently been the sole and primary indication for surgical intervention. The purpose of the present paper was to review the experience with 10 frontal sinus osteomas managed expectantly over the past 11 years. All were imaged serially with morphologic studies, including conventional X-rays and computerized tomography scans. A radionuclide bone scan was carried out in all patients at the time of initial presentation. Those identified as producing mechanical complications clinically, or a 'hot' bone scan by radionuclide study, were regarded as appropriate for osteoplastic frontal sinusectomy for removal of the osteoma; three cases were approached in this way. On the other hand, utilizing this physiologic imaging parameter, a 'cold' bone scan indicated the presence of a relatively insert osteoma, in terms of biologic growth activity. Thus, adopting a non-operative approach, and following these patients over the 4-11 year period appears to have been validated.(ABSTRACT TRUNCATED AT 250 WORDS)