Prader-Willi syndrome (PWS) is a neurogenetic disorder that results from the absence of a normal paternal contribution to the 15q11–13 region1–3. The clinical manifestations of PWS are a transient severe hypotonia in the newborn period, with mental retardation, hypogonadism and obesity observed later in development4. Five transcripts with exclusive expression from the paternal allele have been isolated, but none of these has been shown to be involved in PWS5,6. In this study, we report the isolation and characterization of NDN, a new human imprinted gene. NDN is exclusively expressed from the paternal allele in the tissues analysed and is located in the PWS region. It encodes a putative protein homologous to the mouse brain-specific NECDIN protein7, NDN; as in mouse, expression in brain is restricted to post-mitotic neurons. NDN displays several characteristics of an imprinted locus, including allelic DNA methylation and asynchronous DNA replication. A complete lack of NDN expression in PWS brain and f ibroblasts indicates that the gene is expressed exclusively from the paternal allele in these tissues and suggests a possible role of this new gene in PWS.