A posterior and/or ethmoidal mucocele remains a rare occurrence. The condition usually follows a past history of sinonasal surgery. Extension of the lesion may have ophtalmological implications, with the possibility of causing visual impairment. The predilection for a site of origin in the posterior sinuses explains the frequent absence of nasal symptoms, and the usual pattern of discovery by the ophtalmologist. Modern imaging techniques, especially scanning, allows the diagnosis to be made immediately after the first orbital symptoms. By the same token, recent techniques of endoscopic endonasal surgery have radically changed the treatment. Early complete surgical removal holds out hope for remission of the symptoms that led originally to discovery of the mucocele. We report here a case of posterior ethmoidal mucocele causing a visual field defect which reversed completely after endoscopic treatment.