Our patient (M.S.) had an abrupt onset of amnesia due to a respiratory arrest at the age of 8 years and has been followed by one of us (A.L.R.) for 19 years. A specially designed MRI study indicated that the neuroanatomical localization of his lesion is restricted to the hippocampal formation bilaterally. Comparison of M.S.'s present IQ and academic scores with earlier scores revealed that his literacy skills, certain basic language functions and vocabulary development were arrested by his memory disorder. In contrast, development of mathematical skill was less curtailed, and verbal and nonverbal logical abilities developed to adult levels. Neuropsychological examination at the age of 27 years elicited a pattern of memory deficits similar to those found in a case (H.M.) of known mesial temporal lobe damage in adulthood. The neuropsychological pattern revealed those aspects of cognitive development that do, and those that do not, require intact memory. The limitations to intellectual development imposed by severe amnesia in childhood are not pervasive, but rather, are limited to specific types of abilities.