Two patients are reported with West syndrome associated with hyperlexia. They had peculiar linguistic and psychosocial development and autistic behavior, yet began to read Japanese and Chinese characters, numbers, Roman alphabet letters, and trademark letters at 3 years of age. Neuropsychologic, electroencephalographic, and radiologic studies were performed at 11 years of age in Patient 1 and at 10 years of age in Patient 2. Although they were able to read fluently with correct intonation, their comprehension was significantly impaired. The neuropsychologic evaluation of both patients demonstrated selective, excellent ability in auditory memory in contrast to impairment of associational abilities, visual retention, and visual constructional abilities. These findings suggest that the functions in the nondominant hemisphere were also impaired. Although children with West syndrome frequently have associated mental retardation, patients with West syndrome associated with hyperlexia have never been reported. A neuropsychologic investigation of epileptic children with mental retardation is necessary for the detection of hyperlexia.