The non-Hodgkin's lymphomas (NHL) occurring in children are described on the basis of the Kiel classification. As a rule, the NHL in children are of high-grade malignancy. The morphologic and immunologic features of all types of high-grade malignant B-cell lymphoma are described. The most frequent type of B-NHL in children is B-lymphoblastic lymphoma, including Burkitt and non-Burkitt types. Centroblastic lymphoma, immunoblastic lymphoma and unclassified high-grade malignant NHL are less common in children. The difference between the morphologic term "unclassified" and the immunologic definition "non-B/non-T" or "null" (or "unclassified") is explained. The equivalents of the various lymphoma types in the Lukes-Collins and Rappaport classifications are given.