The malignant non-Hodgkin's lymphomas of childhood are of highgrade malignancy only. There are lymphoblastic and immunoblastic forms. The lymphoblastic lymphomas can be of the Burkitt type (B-cell-derived) or of the "convoluted" or acid phosphatase type (T-cell-derived). A larger number of the lymphoblastic lymphomas are "unclassified" and usually do not belong to either the B-or the T-cell system (stem-cell-derived?). Most of the immunoblastic lymphomas (previously called "reticulosarcomas") are derived from the B-cell series. Besides the lymphomas in the actual sense, there are also true histiocytic reticulosarcomas of childhood. Hodgkin's disease is probably more common in childhood than all of the non-Hodgkin's lymphomas combined.