Abstract: ObjectiveTo explore the clinical characteristics, treatment patterns and prognostic factors of primary mediastinal large B cell lymphoma( PMLBCL). MethodsClinical records of 25 PMLBCL patients who were admitted at department of lymphoma of Tianjin medical university cancer hospital, from October 1999 to May 2009, to evaluate the influence of clinical characteristics and treatment modality on survival. ResultsThe 5-year overall survival(OS) and progress free survival（PFS）were 56.7% and 54.7%, respectively. Eighteen patients accepted chemoradiotherapy and 7 patients accepted chemotherapy alone. The 2-year PFS were 57.1% and 53.6%, respectively, the outcome had not significant difference（P>0.05）. In univariate analysis, only international prognostic index（IPI）and LDH≥2ULN （upper limit of normal）were found to be the prognostic factors associated with overall surviva1 in PMLBCL. But in multivariate analysis, neither were independent prognostic factors. ConclusionIPI and LDH≥2ULN were associated with the prognosis of PMLBCL. But neither was independent prognostic factors in PMLBCL.Compared with chemotherapy, chemoradiotherapy did not show a better response.