Mucocele of the paranasal sinuses is a rare disease not infrequently associated with massive bone destruction, orbital and intracranial complications. The authors report a patient presenting with the giant post-traumatic frontal mucopyocele associated with the erosion of the posterior and inferior sinus walls that was clinically manifested as hypo- and exophthalmos and has caused the inferolateral eye deviation and orbital decompression. The patient displayed the ophtalmological symptoms 8 years after the frontal sinus fracture. The mucopyocele was treated effectively with the combination of the endoscopic trans-ethmoidal and open trans-frontal approaches. The noticeable intraoperative finding in this patient was the absence of complaints as well as the combination of dura mater defects in the form of its erosion and the leakage of the cerebrospinal fluid together with the presence of purulent discharge in the sinus in the absence of intracranial complications.