VEPs to different spatial frequencies (1,2,4 cycles per degree) and different stimulus configurations (vertical, horizontal gratings and checkerboard) were recorded in 47 Multiple Sclerosis patients and a corresponding group of control subjects. Serial recordings were performed in periods of 1-6 years. We show that the highest diagnostic yield in MS is for VEPs of higher spatial frequency than 1 cpd, and that vertical gratings give reliable results when high spatial frequencies are used, whereas checkerboard stimuli elicit consistent VEPs only when the check size is 30'-15' of arc of visual angle. The use of fine vertical grating patterns dissipates controversies dependent on "W" shaped VEPs.