The aim of the present study was to develop a neuropsychological test battery for patients with juvenile neuronal ceroid lipofuscinosis (JNCL) and to study the development of cognitive functions during the first 5 years after diagnosis. Fourteen patients with JNCL entered the study. Nine patients were homozygous for the major mutation, whereas five were compound heterozygotes. All patients were studied annually with a special neuropsychological test battery (NEPSY) adapted from Luria's neuropsychological test, and modified for the visually handicapped; the Wechsler Intelligence Scale for Children - Revised (WISC-R) was also included. The neurological examinations were scored. Furthermore, 1.OT magnetic resonance imaging scan was performed at the beginning of follow-up and after a mean of 5 years. A decline in verbal IQ (WISC-R) during the follow-up period was found in all subjects except one compound heterozygous male. Short-term memory and digit memory span were already impaired at an early stage of the disease. Orientation to time was found to decline more than orientation to person and place. Motor speed usually became impaired after 10 years of age. Spatial orientation was impaired only in the patients homozygous for the major mutation. The test battery was found to be reliable and easy to use, and offered valuable information on the progress of the disease. It also provided important guidelines for rehabilitation.