Six patients with juvenile neuronal ceroid-lipofuscinosis (NCL) who were demonstrated to have abnormally low levels of membrane phospholipids were treated by dietary supplementation with polyunsaturated fatty acids (PUFAs) for periods ranging from 4 years 10 months to 7 years 3 months. Annual evaluations of intelligence and fine motor ability were undertaken while on supplementation. Mental development remained stable in most subjects throughout this period; fine motor function and vision were stable in the two youngest subjects only. These data suggest that PUFA supplementation may arrest the natural course of juvenile NCL if treatment is started early. A larger, multicenter, controlled trial is warranted.