PURPOSE: To delineate chronological changes of cortical hyperexcitability by long-term follow-up of the amplitudes of somatosensory evoked potentials (SEPs) in patients with Japanese Unverricht-Lundborg disease (ULD). METHOD: SEPs to median nerve stimulation were repeatedly examined in 7 genetically diagnosed ULD patients with the mean interval of 11.9 years. The degree of temporal changes in the amplitude of 3 early cortical components, N20, P25 and N35, to the age was analyzed and compared with that of healthy subjects. RESULTS: Their clinical course was almost stable during the follow-up period, namely cessation of generalized tonic-clonic seizures and little or no progression of myoclonus. SEP amplitudes of P25 and N35 were enlarged in all patients and were gradually decreased with aging in ULD on average. The degree of temporal changes of P25 and N35 in ULD was similar or even lower than that of healthy subjects. CONCLUSION: Enlarged but relatively stable SEP amplitudes had a consistency with so-called self-limited clinical course in Japanese ULD. SEP amplitude could be one of the surrogate markers of the degree of cortical hyperexcitability in ULD during the long-term follow-up period.