In current theories of sinusitis, obstruction at the ostiomeatal complex leads to localized inflammation and infection. Haller cells, an extension of ethmoid pneumatization along the maxillary antrum roof, have also been suggested as a causative factor in sinusitis because of their ability to cause narrowing of the infundibulum. Coronal CT scans were reviewed in 154 patients to evaluate the role of Haller cells in sinusitis. Haller cells were present in 34% of patients. The cells were graded as small, medium, or large, and correlated with radiologic evidence of sinusitis (e.g., mucosal thickening or opacification). A statistically significant increase in maxillary sinus mucosal disease was noted in patients with medium or large Haller cells (45.8%) versus those with small cells (28.9%, p < 0.05). Thus obstructive medium and large Haller cells may be an etiologic factor in sinusitis.