Cortical visual impairment (CVI) refers to bilateral impairment of vision that is usually due to damage occurring perinatally in the visual cortex and/or optic radiations. The most common cause of this damage is hypoxia, and other causes include encephalitis, meningitis, and trauma. Relatively little research has been done to quantify visual abilities in children with CVI. In the present study, we used an electrophysiological technique (visual evoked potentials) to measure two aspects of spatial vision in 35 infants and children with CVI (15 females, 20 males; mean age 3 years 6 months, SD 3 years 5 months; age range 4 months to 16 years). We measured each child's grating acuity (resolution for detecting high-contrast stripe patterns) and vernier acuity (resolution for localizing pattern elements). Performance on grating acuity and vernier acuity in individuals with CVI was compared with that of age-matched individuals with normal vision, and it was found that vernier acuity was relatively lower than grating acuity in children with CVI. Results support the theory that vernier acuity is cortically mediated, and suggest that vernier acuity is a more sensitive measure than grating acuity for quantifying vision deficits in patients with CVI.