In a previous study we demonstrated high expression of the non‐coding BIC gene in the vast majority of Hodgkin's lymphomas (HLs). Evidence suggesting that BIC is a primary microRNA transcript containing the mature microRNA‐155 (miR‐155) as part of a RNA hairpin is now accumulating. We therefore analysed HL cell lines and tissue samples to determine whether miR‐155 is also expressed in HL. High levels of miR‐155 could be demonstrated, indicating that BIC is processed into a microRNA in HL. Most non‐HL subtypes were negative for BIC as determined by RNA‐ISH. However, in diffuse large B cell lymphoma (DLBCL) and primary mediastinal B cell lymphoma (PMBL), significant percentages of positive tumour cells were observed in 12/18 and 8/8 cases. A higher proportion of tumour cells were positive for BIC in DLBCL with activated B cell‐like phenotype than in DLBCL with germinal centre B cell‐like phenotype. Differential BIC expression was confirmed by qRT‐PCR analysis. Northern blot analysis showed expression of miR‐155 in all DLBCL and PMBL derived cell lines and tissue samples analysed. In summary, we demonstrate expression of primary microRNA BIC and its derivative miR‐155 in HL, PMBL and DLBCL. Copyright © 2005 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.