Visual evoked potentials recorded from the vertex were studied in seventy four individuals with mental retardation，ranging from l old to 50 years old. They were classified into 4 groups according to the level of IQ/DQ，and the relation between the late components and the intellectual level was exarnined. In 9 of 74 cases(12.2%)，la tency of the N130 component was prolonged and in 7
of 74 cases (9.6%)，the P190 component was prolonged. There was，however，no correlation
between the number of the cases with prolonged N130 or P190 latency and the level of IQ/DQ.
Cases with prolongation in N130 and/or Pl90 were almost exclusively found among those with such complications as cerebral palsy and/or epilepsy，while few cases without complications
showed prolongation. From these results，it is suggested that the prolongation in the late components developes reflecting the presence of the organic lesions that have a common causative
potent producing cerebral palsy and/or epilepsy.