Odontogenic keratocyst (OKC) with secondary inflammation involving the maxillary sinus was presented. Radiological diagnosis of this case was made based on the various findings from the cone-beam computed tomography, computed tomography and magnetic resonance images. There were calcified materials and impacted tooth within the lumen of the lesion, which is not uncommon in OKC. Histopathologic findings confirmed this lesion as OKC with secondary inflammation.