Previous research into the molecular mechanisms that underlie Ag-specific CD8(+) T cell differentiation and function has largely focused on the role of proteins. However, it is now apparent that the mammalian genome expresses large numbers of long (>200 nt) nonprotein-coding RNAs (ncRNAs), and there is increasing evidence that these RNAs have important regulatory functions, particularly in the regulation of epigenetic processes underpinning cell differentiation. In this study, we show that CD8(+) T cells express hundreds of long ncRNAs, many of which are lymphoid-specific and/or change dynamically with lymphocyte differentiation or activation. Numerous ncRNAs surround or overlap immunologically important protein-coding genes and can be predicted to function via a range of regulatory mechanisms. The overlap of many long ncRNAs expressed in CD8(+) T cells with microRNAs and small interfering RNAs further suggests that long ncRNAs may be processed into and exert their effects via smaller functional species. Finally, we show that the majority of long ncRNAs expressed in CD8(+) T cells harbor signatures of evolutionary conservation, secondary structures, and/or regulated promoters, further supporting their functionality. Taken together, our findings represent the first systematic discovery of long ncRNAs expressed in CD8(+) T cells and suggest that many of these transcripts are likely to play a role in adaptive immunity.