The maxillary sinus is a pneumatic space that, when inside it contains foreign bodies, can trigger infections or inflammations of different severities, causing the appearance of cysts, tumors or the development of chronic sinusitis. Imaging is essential for the correct diagnosis of the case, as well as surgical planning for the removal of the foreign body. The present work aims to describe a clinical-surgical case of a patient with an ectopic third molar in the maxillary sinus, emphasizing the clinical, radiographic characteristics, therapeutic conduct and surgical technique, as well as showing the importance of theoretical and practical knowledge regarding the subject. A 49-year-old female patient attended the university’s dental clinic for surgical removal using the Caldwell-Luc technique of the ectopic upper third molar in the left maxillary sinus. The surgical removal of the ectopic element in the maxillary sinus was effective in the case presented, preventing the patient from future pathologies that could affect the sinus, as well as the symptomatological reduction of sinusitis.