We report the first observation of a chromosome abnormality in a patient with typical juvenile ceroid-lipofuscinosis (NCL), who was found to have an apparently balanced translocation between chromosomes 10 and 18 [t(10;18)(q22.1;q21.1)]. Since juvenile NCL was previously mapped to 16p12, this report raises the possibility of heterogeneity in this form of NCL. (C) 1995 Wiley-Liss,Inc.