The aim of the present study was to measure visual acuity (VA) by the sweep visual evoked potential method (sVEP) and relate it to the degree of motor impairment in children with spastic cerebral palsy (SCP). Monocular VA was estimated in 37 SCP children aged from 6 to 48 months, classified as tetraplegic (n = 14), diplegic (n = 13), and hemiplegic (n = 10), without ophthalmological complaints with ages ranging from 6 to 48 months. Motor impairment was rated according to the Gross Motor Function Classification System (GMFCS), in five levels of severity. VA was below age norms in 13/14 (92%) tetraplegics, 10/13 (77%) diplegics and 4/10 (40%) hemiplegics. In addition, a two-way ANOVA within each subgroup showed significant differences in VA between the five GMFCS levels, with high positive correlation between VA loss and the GMFCS rating. Differences between the three types of SCP impairment in each level of GMFCS were not statistically significant, possibly due to the small number of patients. In conclusion, the use of an electrophysiological method (sweep-VEP) for the measurement of visual acuity in these patients allows a more precise and reliable estimate than behavioral measurements, since their motor impairment might interfere with the behaviorally assessed visual acuity. In addition, the finding of a high correlation between quantified motor impairment and VA loss in SCP patients is a new observation that might help to understand the causes of VA loss in these patients.