Mucocele of the paranasal sinus is a cystic lesion with accumulation of mucus within the sinus walls, which is capable of expansion. The frontal sinus is most commonly involved, whereas ethmoidal, sphenoid, and maxillary mucoceles are rare. The floor of the frontal sinus is shared with the superior orbital wall, which explains orbital displacement in enlarging frontal mucoceles. This article presents a case of a spontaneous right frontoethmoidal mucocele with non-axial proptosis in a 26-year-old male patient who was referred by an ophthalmologist to our ENT (ear, nose, throat) clinic for a biopsy to rule out a sinonasal malignancy. An intranasal endoscopic approach was done to obtain a tissue biopsy in a clinic setting, which turned out to be a both diagnostic and therapeutic procedure with complete resolution of symptoms.