The grating acuity of preterm infants was determined by measurements of the visual evoked potential (VEP) produced by phase alternation of sinusoidal luminance gratings. The development of visual acuity in healthy preterm infants appears to be accelerated when compared with full term infants of the same post-conceptual age. Cortical insults and the more advanced stages of retinopathy of prematurity may adversely affect acuity development as indexed by the VEP. Preterm twins also appear to have lower acuity than preterm monoparous infants.