Introduction and importance: Synovial sarcoma is a malignant soft tissue tumor primarily affects the extremities. Its presence in the paranasal sinuses, especially within the ethmoid sinus, is exceedingly rare.

Case presentation: We report a case of monophasic synovial sarcoma of the ethmoid sinus in a 54-year-old woman, who presented with 3 months history of left eye pain and bulging. CT with contrast, MRI, and histopathology confirmed the diagnosis. Whose management was partial surgical resection with postoperative chemotherapy and radiotherapy. Post-treatment, the patient showed a good clinical outcome and remained under regular follow-up care by the oncology team.

Case discussion: To our knowledge, there are only six reported cases of primary synovial sarcoma in the ethmoid sinus. Its atypical presentation and unspecific features make diagnosis challenging. Partial surgical resection with postoperative chemotherapy and radiotherapy is the standard treatment. However, the prognosis remains poor, with a high risk of recurrence, necessitating thorough follow-up.

Conclusion: This case highlights the presentation and management of a significantly rare tumor in unusual body region.