Primary mediastinal large B cell lymphomas (MLCL) differ from other diffuse large cell lymphomas, leading to a description as a separate entity in the current World Health Organization classification. Dose intensification improves long-term results, but no standard therapy has been established so far. We investigated the use of a high-dose methotrexate-based alternating chemotherapy regimen (B-ALL protocol of the German ALL study group) followed by consolidative mediastinal radiotherapy first as a single-center trial, then later as a prospective multicenter trial in 44 patients with a median age of 33 years. Response rates exceeded 90% with an overall survival rate of 80% in the single-center group (8.6 years median follow-up) and 82% in the multicenter group (2.5 years follow-up).Short-term toxicity was manageable, but required hospitalization: the rates of grade 3 or 4 toxicity were 20% (for mucositis), 42% (for neutropenia), 29% (for thrombocytopenia), and 9% (for neutropenic fever). No relapse occurred more than 2 years after diagnosis and initiation of treatment, but unfortunately, no patient with overt progression or relapse within these 2 years could be salvaged. Future directions in the treatment of MLCL will not focus on further dose intensification, but rather on the incorporation of (radio)immunotherapy as a therapeutic tool and gene expression profiling as well as positron emission tomography-computed tomography as stratifying tools.