Osteomyelitis is an acute or chronic inflammatory process that can involve cortical and trabecular aspects of bone or bone marrow. Cranial bones are infrequently involved, but spreading of inflammation with involvement of surrounding structures represent important risk, as are cerebral abscess, encephalitis, or meningitis. We present a case of osteomyelitis of right maxillary sinus in an adult caused by a spreading of contiguous inflammation sustained by a chronic intrasinusal polyp; the complete resolution of infection was gained with a combination of surgical treatment and antibiotic therapy. The aims of this article are to illustrate diagnostic patterns and surgical treatment experienced in a case of maxillary osteomyelitis and to report radiographic and histopathologic findings.