This dataset contains more than 900 unique ncRNA sequences which have been identified and manually curated based upon extensive literature review. The majority of ncRNAs listed here are much longer than those in the previous three datasets. Altogether, 36 mammalian organisms are represented but most ncRNAs are either murine or human. Although some of these transcripts have documented biological roles, most are transcripts of unknown function. As well as sequence data, additional information - including Genbank accessions, references, chromosomal location, transcript length, splicing status, conservation notes, function, disease associations, antisense relationships, imprinting status, and tissue expression patterns - is provided wherever possible in separate searchable fields.