MicroRNA miR-155 is processed from sequences within BIC RNA, a non-coding RNA that accumulates in B cell lymphomas. The precursor of miR-155 is likely a transient spliced or unspliced nuclear BIC transcript, not the cytoplasmic BIC RNA. Clinical isolates of several B cell lymphomas, including diffuse large B cell lymphoma (DLBCL), have 10- to 30-fold higher copy numbers of miR-155 than normal B cells. BIC RNA levels are also elevated in lymphoma cells, but the ratio of miR-155 to BIC RNA varies, suggesting miR-155 levels are controlled by transcription and processing. DLBCLs with an activated B cell phenotype have significantly higher miR-155 levels than those with a germinal center phenotype, which is associated with poorer clinical outcomes. Quantifying miR-155 may be useful for diagnosis. BIC RNA is spliced and polyadenylated, likely generated by RNA polymerase II, but lacks long ORFs. A mouse miRNA, miR-155, is encoded within the conserved region of BIC RNA. miRNAs, including miR-155, function in post-transcriptional gene regulation. In animal cells, miRNAs are processed from primary transcripts by Drosha and DICER. The conserved region of BIC RNA can form an imperfect hairpin structure, suggesting miR-155 is generated by this pathway. Changes in miRNA levels can affect cancer progression. miR-155 levels are elevated in DLBCLs with an activated B cell phenotype, which has a worse prognosis. BIC RNA and miR-155 levels are increased in clinical lymphoma isolates, with miR-155 levels being 2- to 3-fold higher in ABC phenotype DLBCL cells than in GC phenotype cells. Quantification of miR-155 may be useful for diagnosis. BIC RNA and miR-155 were quantified in lymphoma cell lines and clinical isolates using Invader assays. BIC RNA is primarily cytoplasmic and not a precursor for miR-155. miR-155 is processed from nuclear BIC transcripts. The levels of miR-155 and BIC RNA in lymphoma cells are significantly higher than in normal B cells. miR-155 levels are higher in ABC phenotype DLBCL cells than in GC phenotype cells. miR-155 may be a useful diagnostic marker for DLBCL. The levels of miR-155 and BIC RNA in lymphoma cells are significantly higher than in normal B cells. miR-155 levels are higher in ABC phenotype DLBCL cellsMicroRNA miR-155 is processed from sequences within BIC RNA, a non-coding RNA that accumulates in B cell lymphomas. The precursor of miR-155 is likely a transient spliced or unspliced nuclear BIC transcript, not the cytoplasmic BIC RNA. Clinical isolates of several B cell lymphomas, including diffuse large B cell lymphoma (DLBCL), have 10- to 30-fold higher copy numbers of miR-155 than normal B cells. BIC RNA levels are also elevated in lymphoma cells, but the ratio of miR-155 to BIC RNA varies, suggesting miR-155 levels are controlled by transcription and processing. DLBCLs with an activated B cell phenotype have significantly higher miR-155 levels than those with a germinal center phenotype, which is associated with poorer clinical outcomes. Quantifying miR-155 may be useful for diagnosis. BIC RNA is spliced and polyadenylated, likely generated by RNA polymerase II, but lacks long ORFs. A mouse miRNA, miR-155, is encoded within the conserved region of BIC RNA. miRNAs, including miR-155, function in post-transcriptional gene regulation. In animal cells, miRNAs are processed from primary transcripts by Drosha and DICER. The conserved region of BIC RNA can form an imperfect hairpin structure, suggesting miR-155 is generated by this pathway. Changes in miRNA levels can affect cancer progression. miR-155 levels are elevated in DLBCLs with an activated B cell phenotype, which has a worse prognosis. BIC RNA and miR-155 levels are increased in clinical lymphoma isolates, with miR-155 levels being 2- to 3-fold higher in ABC phenotype DLBCL cells than in GC phenotype cells. Quantification of miR-155 may be useful for diagnosis. BIC RNA and miR-155 were quantified in lymphoma cell lines and clinical isolates using Invader assays. BIC RNA is primarily cytoplasmic and not a precursor for miR-155. miR-155 is processed from nuclear BIC transcripts. The levels of miR-155 and BIC RNA in lymphoma cells are significantly higher than in normal B cells. miR-155 levels are higher in ABC phenotype DLBCL cells than in GC phenotype cells. miR-155 may be a useful diagnostic marker for DLBCL. The levels of miR-155 and BIC RNA in lymphoma cells are significantly higher than in normal B cells. miR-155 levels are higher in ABC phenotype DLBCL cells