Visual masking assesses visual perception and attention; it occurs when a visual stimulus (mask) interferes with the perception of a stimulus that the participant is trying to identify (target). A backward masking study (target presented before mask) was performed on 662 children without disabilities (338 females), aged between 6 and 17 years, in order to evaluate if performance varies with age. In the masking procedure 10 letters were presented through a tachistoscope as target stimuli. Fragments of letters oriented at random (‘noise’) represented the mask. A slight improvement of visual performance from the beginning of school age to 9–12 years of age was found. This paper gives normative data for the most important parameters which can be used as a standardized reference for the procedure employed. We also studied 113 children with epilepsy (56 females), aged between 5 and 19 years, who attended a mainstream school and had been seizure free for at least 2 years. Children were tested just before starting antiepileptic drug withdrawal and re-tested 1 year later; they were drug free for 3 months before the second test. These children showed, during and after treatment, only slightly worse results when compared with healthy children of the same age; after therapy withdrawal, their visual performance slightly improved but this was not statistically significant.