Odontogenic keratocyst is a benign intraosseous lesion of odontogenic origin which is characterized by its aggressive nature. It is usually present in the mandibular posterior area, although it can also be found in the maxilla, particularly in the canine region. We discuss a unique example of OKC in the maxillary sinus involving the 27&28 region. Due to comparable clinical signs, this lesion is more prone to be mistaken for other lesions of the maxillary sinus, such as sinusitis or polyps. On the other side, this benign disease has the potential to develop into Ameloblastoma or squamous cell carcinoma. A favorable prognosis thus depends on early identification, precise diagnosis, appropriate treatment, and follow-ups.