Out of a series of 427 NHML based on the Kiel classification and without previous treatment, 186 were of high grade malignancy and among them were 83 lymphoblastic (LB) and 58 immunoblastic (IB) lymphomas which were included in this study. The LB and IB, which represent the majority of high grade NHML, were compared regarding their clinical features and courses. Eight main criteria were significantly different between these two groups: age of patient, immunological history, mediastinal and pleural involvement, primary or secondary involvement of the bone marrow, secondary leukaemia, secondary meningeal involvement, and involvement of the facial region. Some of these differences (mediastinum and meningeal involvement) are related to subtypes within LB. The differences between these two groups suggest that different treatment programs may be warranted.