The aim of the present research was to evaluate the prognostic value of the Kiel classification of malignant non-Hodgkin's lymphomas. For this purpose a series of 100 consecutive, previously untreated adults with advanced malignant non-Hodgkin's lymphomas was analyzed. The median age of the patients was 54 years; 61 patients were males. Although the number of the various groups considered was limited, a statistically significant difference (p less than 0.001) was found in the median survival of patients with lymphomas of low-grade malignancy (lymphocytic, lymphoplasmacytoid, centrocytic, centroblastic-centrocytic lymphoma) and lymphomas of high-grade malignancy (centroblastic, lymphoblastic, immunoblastic lymphoma). A difference in survival (p less than 0.001) was also observed among the patients with lymphocytic lymphoma and those with centroblastic-centrocytic lymphoma, whereas no significant difference in survival was found between the histological subtypes of high-grade malignant lymphomas. Our observations support the opinion that the Kiel classification is useful in clinical practice to distinguish the histological types with a better prognosis from those with a worse one; in addition this classification appears to be of conceptual value.