AIM:To study morphoimmunological and clinical features of primary mediastinal large B-cell lymphoma (PMLBCL).MATERIAL AND METHODS:We analysed the results of biopsy material study and treatment of 86 PMLBCL patients, effects of different factors on the disease prognosis, efficacy of some therapeutic programs and overall therapeutic efficacy.RESULTS:PMLBCL manifests mainly with massive lesions of anterior upper mediastinum with involvement of adjacent organs and tissues, absence of bone marrow involvement, frequent affection of CNS. Many primary patients have resistance to treatment, sensitive patients have no late recurrences.CONCLUSION:PMLBCL is an independent extranodal variant of non-Hodgkin's lymphoma with special clinical and morphoimmunological characteristics. Criteria are proposed for differential diagnosis of different variants of PMLBCL. New approaches to PMLBSL patients' management are outlined.