This case report discusses a 52-year-old lady with nonaxial proptosis, diplopia and diminution of vision due to a mass lesion in the upper medial quadrant of the orbit. A computed tomography scan revealed a well-defined lesion in the frontal sinus area with orbital and intracranial extension. On exploring it was found to be a mucopyelocele of the frontal sinus. Surgical excision was done by an external approach. The symptoms and signs resolved completely within a week. Frontal sinus mucopyeloceles are benign and curable, and their early recognition and management is of paramount importance, because they can expand and cause orbital as well as intracranial complications.