Twenty boys meeting the current DSM III criteria for infantile autism at the time of diagnosis were found to be hyperlexic in childhood and have been followed up for 7-17 years. The most striking feature of the group was the compulsion to decode written material without comprehension of its meaning, and this constituted a behavioral phenotype for this population. On word recognition tests such as the WRAT, they scored significantly higher than would be predicted on the basis of intelligence but demonstrated severe reading retardation on tests of reading comprehension such as the Gates-McGinitie. Major differences in intelligence were detected, ranging from severe mental retardation to very superior intelligence. Major differences in verbal and nonverbal abilities were also noted. Many were found to have unusually good memory, both visual and auditory, and the majority possessed an excellent stored vocabulary that could be used with written words despite the poverty of their expressive language. It is suggested that the presence of hyperlexia may identify a subgroup of autistic children.