Five squirrel monkeys were monocularly deprived at birth for 3 years. Visual field testing for the deprived eye revealed no responses to visual stimuli at any position, including the monocular segment. These results are similar to those obtained in macaque monkeys after long-term neonatal monocular deprivation and indicate that lack of patterned visual input to an eye during development in primates can produce functional blindness throughout the visual field. Because the monocular segment of the visual field was not spared, binocular competition cannot be the only mechanism underlying this loss. Instead, lack of patterned visual input probably causes improper neuronal connections during development in all segments of the visual cortex resulting in complete loss of form vision.