['Expression patterns of microRNAs in serum are involved in potentially biomarkers for various diseases. The aim of the study was to investigate the expression level of miR-21 in diffuse large B cell lymphoma (DLBCL) and its prognostic value.', 'Real-time quantitative polymerase chain reaction (qRT-PCR) was used to measure miR-21 levels in serum samples from 112 patients with DLBCL as well as in serum samples from 45 healthy controls. The associations between miR-21 expression and clinicopathologic parameters and overall survival of the patients, were analyzed by chi-square test and Kaplan-Meier method. The Cox proportional hazards regression analyses were performed to estimate the prognostic values for patient survival prediction.', 'We found that serum miR-21 expression was markedly upregulated in patients with DLBCL than healthy controls. Increased miR-21 expression was significantly correlated with B symptoms, IPI score, CHOP-like treatment and Rituximab (all Ps<0.05). Moreover, DLBCL patients with miR-21 higher expression have shown significantly worse overall survival than those with lower miR-21 expression. And miR-21 expression was an independent prognostic marker of overall survival in a multivariate analysis (P=0.001, HR: 4.404, 95% CI: 1.770-10.956).'] Does miR-21 expression predict prognosis in diffuse large B-cell lymphoma?