Pupil asymmetry or anisocoria can have benign or malignant causes, and be categorized as acute or chronic. It can also be a normal finding in about 20% of cases. Benign episodic unilateral mydriasis is an isolated benign cause of intermittent pupil asymmetry. The exact pathophysiology is not always understood. According to one hypothesis, it is due to discordance between the sympathetic and parasympathetic systems. It is occasionally seen in patients with migraine. Some authors consider it a limited form of ophthalmoplegic migraine. We report a case of benign episodic unilateral mydriasis diagnosed in a 30-year-old lady with a history of migraine who had extensive negative neurological evaluation.