To investigate the etiology of bilateral disc swelling in Japanese.Using Kitasato University's Department of Neuro-Ophthalmology medical records and fundus photographs of the period December 1977 through November 2010, we retrospectively identified 121 outpatients who had been initially confirmed with bilateral disc swelling.The most common cause of the bilateral disc swelling was increased intracranial pressure (ICP) (59%); followed by pseudopapillitis (16%); uveitis (8%); hypertensive retinopathy (5%); bilateral optic neuritis, acute disseminated encephalomyelitis (ADEM) and optic disc drusen (all at 2% each); and leukemia (1%). Unknown etiology accounted for 6% of the cases.Although increased ICP is the most common etiology for bilateral disc swelling, it can also be triggered by a variety of other causes. Pseudopapillitis is the most important progenitor of bilateral disc swelling in Japanese.