The objective of the present study was to examine the impact of acute undernutrition on polar visual contrast sensitivity (CS) in children. Undernutrition is a nutritional inadequacy that impairs many cognitive functions, including visual perception. Acute undernutrition refers to a current nutritional inadequacy that is related to low body weight according to height and age. We measured polar visual CS in 30 children of both sexes, aged 8 to 10 years. Fifteen eutrophic children constituted the control group (CG), and 15 acute undernourished children constituted the experimental group (EG). The children’s nutritional status was classified according to Waterloo’s anthropometric parameters and confirmed by records from the State Health Care System. Contrast sensitivity was measured using a 2-alternative forced-choice psychophysical method at a distance of 150 cm from the stimuli, binocularly, with a mean luminance of 40.1 cd/m2. One-way analysis of variance was applied, revealing significant differences between groups (F4,145 = 11.25, p < .05). Fisher’s least significant difference analysis revealed significant differences between groups at spatial frequencies of .25, 1.0, and 2.0 cycles per degree (cpd; p < .05). The CG was 33%, 53%, and 28% more sensitive than the EG in the detection of the .25, 1.0, and 2.0 cpd spatial frequencies, respectively. These results suggest that acute undernutrition reduces polar CS function in children. Therefore, acute undernutrition, which is known to affect primary visual cortical areas, may also affect higher visual cortical areas, such as V4 and the inferotemporal cortex.