OBJECTIVE: To report a case of a patient with peritonsillar myiasis whose initial clinical diagnosis was a peritonsillar abscess. CASE REPORT: A 73-year-old diabetic woman with a 3 year history of cacosmia and serous nasal crusts visited the otolaryngology service with a 4 day history of fever, malaise, and sore throat that made it difficult to swallow. Physical examination revealed significant bulging and redness in the left peritonsillar region. She was alert, afebrile, oriented, and cooperative, with crackles in both lung bases and otoscopy showing mucopurulence in the left external auditory canal. The oral bulging was punctured and showed no secretions. Within hours, the patient's state evolved with signs of septicemia, a decreased level of consciousness, and blood desaturation; she was referred to the intensive care unit (ICU) the next day, requiring orotracheal intubation. She underwent a new puncture, obtaining negative results, but larvae were observed in the left posterior tonsillar pillar and left nostril minutes after the procedure. A radiograph of the chest revealed bilateral pulmonary infiltrates in the lower third. Iodoform was applied to the oral and nasal cavity and ivermectin was administered via an orogastric tube, and broad-spectrum intravenous antibiotics were utilized. During the first 3 days, just over 150 larvae were removed, after which no more larvae appeared. The patient worsened in the first week, requiring vasoactive drugs, but evolved with progressive improvement from the second week on. CONCLUSION: It is important to note the possibility of the diagnosis of myiasis in the nasal cavity and pharynx because of the value of early treatment and to avoid invasion of adjacent structures.