Primary mediastinal large B-cell lymphoma (PMLBCL) is a unique clinico-pathological subtype, for which there is no optimal therapy yet. We evaluated clinical characteristics and prognostic factors in 39 consecutive, previously untreated Chinese patients with PMLBCL. The median age was 28 years (range 16-72 years). The majority of patients were stage I/II (23 cases, 59%). Bulky mediastinal mass was present in 18 cases (46%). The 3-year overall survival (OS) and progression-free survival (PFS) rates were 70 and 64%, respectively. Cox regression analysis showed that low serum albumin was an independent prognostic predictor of both OS (P = 0.002) and PFS (P = 0.001). Other prognostic factors for OS were extra-thoracic involvement (P = 0.016) and B symptoms (with borderline significance, P = 0.053). The addition of radiotherapy to chemotherapy seemed to have a favourable impact on OS (P = 0.034) and PFS (P = 0.039). The addition of rituximab to chemotherapy improved the survival trend, but added no significant benefit (OS: 57 vs. 84%, P = 0.287; PFS: 53 vs. 73%, P = 0.371). Our data additionally suggest that low serum albumin is a novel prognostic predictor for PMLBCL, and could be useful in determining treatment options in the clinic.