Primary mediastinal large-B cell lymphomas (PMLCL) are considered to be a distinct clinicopathologic entity among the diffuse large B-cell lymphomas. This study evaluated the prognostic factors and therapeutic outcome of PMLCL in a single-institution series. Twenty seven patients were reviewed. Nineteen of the 27 had Stage I-II and 8 had Stage III-IV disease. B-symptoms were found in 11 (41%) and bulky disease in 10 (37%) patients. All were initially given combination chemotherapy (CT): doxorubicin-containing regimens to 23 patients (11 patients had CHOP, 12 received more intensive third-generation regimens) and 4 elderly (>70 years) patients received CVP. Eleven responders were consolidated with irradiation (RT) as part of their initial treatment, with a median total dose of 39 Gy. Nineteen patients (70%) achieved clinical remission (15 CR and 4 PR) with their initial therapy. Forty-four percent of patients remained progression-free and 59% are alive at 3 years. The actuarial 10-year time to progression (TTP) and overall survival (OS) were 44% and 50%, respectively. Age >60 years, performance status >1 and IPI intermediate-high to high risk were significantly associated with poorer OS and TTP by univariate analysis (log-rank test). A better outcome was associated with the use of more aggressive chemotherapy regimens or with the inclusion of RT in the first-line treatment. Our analyses suggest that the application of radiotherapy in combination regimens and the use of more aggressive chemotherapy in the treatment of this particular type of lymphoma should now be evaluated in prospective randomized trials.