Twenty patients with melanocytoma of the optic disc underwent Goldmann perimetry and pupillary evaluation. Two patients (10%) had normal visual fields. Three (15%) had minimal blind spot enlargement. Fifteen patients (75%) had a greatly enlarged blind spot, of which ten had concomitant nerve fiber bundle field defects. These consisted of a nasal step in two cases (10%), relative nerve fiber bundle defects in four cases (20%), and an absolute arcuate defect in four cases (20%). The blind spot enlargement relates to the pigmented tumor extended beyond the disc boundary, thereby shading the peripapillary retina. The nerve fiber bundle defects result from injury to the visual axons passing through the nerve head, although the mechanism is uncertain. A Marcus Gunn pupillary sign produced by the melanocytoma was found in six patients (30%), all of whom had a substantial relative or absolute nerve fiber bundle defect.