The clinical courses of 17 JNCL patients were analyzed retrospectively with the use of a simple, disease-specific scoring system. The mean observation period was 14 years (range 8-18 years). Scores of 0 (maximal dysfunction) to 3 (normal function) were assigned to each patient's vision, intellect, language, motor function, and epilepsy for each year of observation. The lapse of medians and ranges of all patients' scores were established from age 3 to 20 years. This scoring system allowed quantitative description of an individual course in context of the wide natural variability of the disease. Patients with seizures starting before the age of 10 years tended to have intractable epilepsy, to receive multiple antiepileptic drug therapies, and to have poor courses including problems not related to epilepsy. One patient had a course clearly outside the usual variability of JNCL and is thought to represent a genetic variant.