Treatment for mediastinal lymphosarcoma was given to 71 patients, aged 3-14 years, at the Institute's Clinics during 1982-1991. In that group, there were more males than females (3.4:1), mean duration of the condition of 3 months, T-cell immunity pattern (89.9%), enlarged anterior mediastinal lymph nodes and thymus, pleural lesions including pleuritis, mean mediastinal-thoracic index of 0.5, compression syndrome, elevated concentration of lactate dehydrogenase and presence of tumor cells in the bone marrow and peripheral blood. Among major negative factors of prognosis were inadequate therapy, pleural lesions and stage IV tumor.