Although benign episodic mydriasis has been rarely reported worldwide, most of the reports so far have occurred in unilaterally. To report an unusual case of benign episodic bilateral mydriasis.

Nineteen-year-old woman who presented with intermittent dilation of both pupils two months ago. She had difficulty on reading and doing tasks because of her visual blur. This symptom usually lasted for 1–2 hours, occurred once every 2–3 days, most frequently during stressful situations. Headaches and dizziness accompanied the eye symptoms, and her pupils were both 5 mm in a lighted room and both 7 mm in a dark room. All tests, including brain magnetic resonance imaging, showed no abnormal findings. We diagnosed her as benign episodic bilateral mydriasis. The frequency of her symptoms decreased during the university vacation period.

In the absence of ophthalmologic or neurologic abnormalities other than headaches in patients with transient mydriasis, benign episodic mydriasis should be considered as a differential diagnosis. Although benign episodic bilateral mydriasis has a unilateral predominance, for the first time the authors report that benign episodic mydriasis may occur in both eyes during same episode.