 The purpose is to test whether early central nervous system CNS prophylaxis given at the beginning of therapy for young high risk diffuse large B-cell lymphoma DLBCL patients is feasible and could reduce the risk of CNS relapses. Early CNS prophylaxis with two courses high dose methotrexate HD-MTX in combination with rituximab-cyclophosphamide-doxorubicin-vincristine-prednison R-CHOP is followed by four courses of R-CHOP14 and etoposide E and one course of HD-Ara-C. In addition the patients will receive three courses of liposomal cytarabine intrathecally. The results will be compared to a recent Nordic CRY-04 study. Shifting of CNS prophylaxis to the beginning of the therapy offers a potential to overcome the subclinical disease and thus reduce the risk of early clinical CNS recurrence. As flow cytometry FCM can improve the sensitivity for detecting occult leptomeningeal disease over cytology , FCM from cerebrospinal fluid will be incorporated into the staging procedures. 