A 53-year-old woman presented with an approximately 5-year history of recurrent headaches, nasal airway obstruction, and discolored nasal discharge. She was treated with multiple antibiotic courses, without noticeable improvement. A computed tomographic scan revealed marked enlargement of the sphenoid sinus (Figures 1, 2, and 3). There was circumferential osteoneogenesis of the sinus wall (Figure 1, arrowheads), but the sinus was completely aerated. The intersinus septum was absent, but both of the sinus ostia were widely patent (Figures 2and 3, arrowheads). Multiple computed tomographic scans performed over several years had similar findings, with variable amounts of fluid in the sinus but never complete opacification.