A retained surgical sponge is an uncommon complication in endoscopic sinus surgery. A 53-year-old woman who underwent endoscopic sinus surgery two years prior presented with nasal stuffiness and posterior nasal dripping that had persisted for one year. On CT images, a soft-tissue mass with mixed high and low attenuation was noted in the posterior air cells of the right ethmoid sinus. CT imaging features of the surgical sponge granuloma are described