Brainstem auditory evoked response and subcortical abnormalities in autism. Previous studies of the neurobiology of autism that have used the brainstem auditory evoked response have given contradictory results. The authors of this study considered two supplementary aspects; they added an ipsilateral masking procedure, and they compared the results for every subject to the values (corrected for age and sex) of a large number of normal children. Twenty autistic (according to DSM-III-R criteria) and 13 mentally retarded (nonverbal IQ less than 75) subjects were assessed. Eighty percent of the autistic subjects had abnormal interpeak latencies, compared to 15% of the mentally retarded subjects. The I-V and III-V prolonged interpeak latency values were seen only in the autistic subjects. The ipsilateral masking procedure doubled the rate of detection of higher-brainstem abnormalities in the autistic children. 