Lymphoblastic lymphoma (LBL) comprises 2% to 4% of non-Hodgkin lymphomas cases in adults, of which 85% to 90% of LBL in adults is of T-cell phenotype. This study was aimed to evaluate the clinical characteristics and prognostic factors of patients with mediastinal T-LBL. Based on the retrospective analysis of the clinical data of 35 patients with mediastinal T-LBL during the period from January 1998 to January 2011, the clinical characteristics and prognostic factors of mediastinal T-LBL were summarized. The results showed that the total of 35 patients were identified (male 24 and female 11), with a median age of 19 (5 - 52) years. The majority of patients were in stage III/IV, 16 cases (45.7%) presented bulky mediastinal mass. Intrathoracic effusions (pleural, pericardial) were not uncommon (62.9%). Overall survival rate (OS) and progression-free survival rate (PFS) at 3 years for the entire cohort were 36% and 24%, respectively. OS and PFS at 5 years were 25% and 16.7%, respectively. Anemia at diagnosis were an important, independent predictor of OS (P = 0.048). Bulky mass (P = 0.048), superior vena cava syndrome (P = 0.021), and abnormal PLT count at diagnosis was the independent prognostic factors for PFS (P = 0.021). It is concluded that the patients with primary mediastinal T-LBL are characterized by a low incidence, bad prognosis, and short survival. For patients accompanying with anemia, bulky mass and superior vena cava syndrome, their prognosis is worse.