We have previously detected a large germ-line deletion, which included the entire p15/CDKN2B-p16/CDKN2A-p14/ARF gene cluster, in the largest melanoma-neural system tumor (NST) syndrome family known to date by means of heterozygosity mapping based on microsatellite markers. Here, we used gene dose mapping with sequence-tagged site real-time PCR to locate the deletion end points, which were then precisely characterized by means of long-range PCR and nucleotide sequencing. The deletion was exactly 403,231 bp long and included the entire p15/CDKN2B, p16/CDKN2A, and p14/ARF genes. We then developed a simple and rapid assay to detect the junction fragment and to serve as a direct predictive DNA test for this large French family. We identified a new large antisense noncoding RNA (named ANRIL) within the 403-kb germ-line deletion, with a first exon located in the promoter of the p14/ARF gene and overlapping the two exons of p15/CDKN2B. Expression of ANRIL mainly coclustered with p14/ARF both in physiologic (various normal human tissues) and in pathologic conditions (human breast tumors). This study points to the existence of a new gene within the p15/CDKN2B-p16/CDKN2A-p14/ARF locus putatively involved in melanoma-NST syndrome families and in melanoma-prone families with no identified p16/CDKN2A mutations as well as in somatic tumors.