Fibrous dysplasia (FD) is a non-malignant bone tumor that typically behaves as a slow and indolent growing mass lesion. We report the case of a female patient presenting with headache and facial deformity and later diagnosed with polyostotic fibrous dysplasia (PFD). A 29-year-old woman visited Mealhada Primary Health Care Unit complaining of headache, nasal congestion, and hyposmia for several weeks. She also presented with facial deformity and painful swelling of the upper left orbit. X-ray imaging revealed a suspicious opacity in the left frontal sinus and a right shift of the nasal septum. Computed tomography and bone scintigraphy later confirmed a tumor involving the ethmoid and frontal bone. The patient was referred to the neurosurgery and otorhinolaryngology departments of a central hospital and the suspected diagnosis of PFD was confirmed. A watchful waiting approach with regular imaging screenings was proposed and accepted by the patient, who is now free of symptoms and more acceptant of the benign condition of her tumor. With this case, we aim to make family physicians more aware of this rare but relevant condition that can be difficult to diagnose. FD is a rare but benign tumor that occurs mainly in adolescents and young adults. Symptoms depend on the location and type of the tumor and include facial deformity, vision changes, nasal congestion, and headache. No clear guidelines exist for its treatment, and options include monitoring the progression of the tumor, in addition to medical or surgical approaches.