In population-based studies and in clinical practice a reliable, objective measure of optic disc cupping is needed. This measure is of special importance when following patients with diagnosed or suspected glaucoma. We have developed a new system using stereoscopic fundus photographs for quantitating optic disc cupping from these photographs. Measurements of the cup are based on cup contour. For this system, measurements of longest and shortest cup and longest and shortest disc diameters by two observers were highly correlated, with correlation coefficients of 0.88, 0.88, 0.77, and 0.82, respectively. Mean cup to disc ratios for long and short disc diameters were within 0.04 (n = 330) between the two observers. The measurements show a high degree of inter- and intra-observer reliability, and are inexpensive in time and materials to perform. This method is well suited to population-based studies.