A 48-year-old man presented with blurred vision of 3 months' duration. The right eye had a narrow band of corneal thinning, measuring approximately 2 mm, and ranging from 4 o'clock to 10 o'clock. The left eye had a wider band of corneal thinning, measuring approximately 2.5 mm, extending from 2 o'clock to 9 o'clock. Pellucid marginal degeneration (PMD) is a rare, mostly nonhereditary, and bilateral corneal condition of unknown origin. Typically, a narrow band of thinning in the cornea, measuring 1-2 mm in width, is detected. This thinning occurs about 1-2 mm from the limbus and runs for a distance of up to 4 clock-hours (typically from 4 to 8 o'clock). PMD may manifest in the superior cornea on rare occasions.