Pattern visual, somatosensory and brainstem auditory evoked potentials (EPs) of 14 patients with definite multiple sclerosis, 222 patients suspected of having multiple sclerosis, 26 patients with isolated optic neuritis and 40 patients with a chronic not diagnosed neurologic disorder, were compared with their clinical diagnoses on 2 1/2-year follow-up. In the MS suspects, an EP abnormality demonstrating a clinically silent lesion in any modality (65 patients) was associated with a 71% chance of clinical deterioration (48% chance of definite MS within the follow-up period). Normal EPs (121 patients) were associated with a 16% chance of deterioration (4% chance of definite MS). EPs in patients in whom the only abnormalities confirmed known lesions (36 patients) did not predict follow-up status. Visual EPs demonstrated clinically silent lesions more frequently than somatosensory and auditory EPs (22%, 12% and 5% of patients). Only one of the patients with optic neuritis and 3 of the chronic not diagnosed group had EPs demonstrating clinically silent lesions. CSF and NMR studies also correlated with follow-up in subseries of the patients.