PIP: The use of B-scan ultrasonography in the diagnosis of oral contraceptive-related optic neuritis is presented. A 23-year-old woman complaining of pain in the right upper eyelid, followed by blurred vision in that eye, of approximately 6 days duration claimed to be in good health and took no medication but an oral contraceptive. In light of visual field changes, noted upon clinical examination, and positive Marcus-Gunn swinging flashlight test results, it was decided to compare optic nerve images with the Bronson-Turner B-scan ultrasonogram. The test disclosed a definite enlargement of the right optic nerve as seen in retrobulbar neuritis (figures included). A tentative diagnosis of optic neuritis secondary to oral contraceptive use seemed born out by the reversion to normal of the optic nerve after discontinuation of oral contraceptive therapy.