We report a patient who presented with acute painful monocular visual loss reminiscent of idiopathic optic neuritis. After treatment with corticosteroids was commenced, an anterior clinoid mucocele causing compressive optic neuropathy was demonstrated on imaging studies. The diagnosis was proven histopathologically following excision of the lesion via craniotomy. Although very rare as a cause of optic neuropathy, anterior clinoid mucocele should be excluded by adequately imaging the optic canal, as visual prognosis is poor if surgical decompression is not performed in a timely fashion.