Although many clinicians believe that there is a racial difference in the size of the physiologic cup, this premise has not been studied. To evaluate this, we prospectively examined 100 black and 100 white volunteers. Stereoscopic optic disc photographs taken of each subject were masked to block out the fundus pigmentation, randomized, and then evaluated by an experienced clinician. The average cup/disc ratio in blacks (0.35) was significantly greater (P less than 0.0001) than that in whites (0.24) for both right and left eyes. Forty percent of the optic discs of blacks and 14% of the optic discs of whites had a cup/disc ratio greater than or equal to 0.4.