A clinicopathologic analysis of 42 cases of non-Hodgkin's lymphoma of the intermediate lymphocytic type (ILL) having morphologic features between those of well-differentiated (WDLL) and poorly differentiated lymphocytic lymphoma (PDLL) is presented. In lymph node sections, ILL was characterized by a diffuse proliferation consisting predominantly of small lymphoid cells with slightly irregular or indented nuclei. A mixture of lymphoid cells with entirely round nuclei and lymphoid cells with angulated and cleaved nuclei was also present, but each of these two cell populations did not comprise more than 30% of the total. The median age of the patients was 65 years, and the male-to-female ratio was 5:1. Generalized lymphadenopathy was evident in 74% of the patients, and B symptoms were presented in 36%. Peripheral blood involvement was present at the onset of disease in 21% of the patients, and the bone marrow was involved by lymphoma in 76% of those examined. Five percent of the patients had Stage I disease, 24% had Stage III disease, and 71% had Stage IV disease. Ninety-three percent of the patients received multiagent chemotherapy and 41% achieved a complete remission. The overall median survival was 31 months. Clinical features which appeared to influence survival adversely included the presence of B symptoms (P = 0.007), age greater than 70 years (P = 0.09), an absolute lymphocyte count above 5000/mm3 (P = 0.05), and anemia (P = 0.09). Achievement of a complete remission influenced survival favorably (P = 0.02). Pathologic features which appeared to influence survival included sinus obliteration, which had an adverse effect (P = 0.05), and the presence of residual germinal centers which had a favorable effect (P = 0.06). Patients with 0-5 mitoses/10 high power fields (HPF) had a significantly longer survival than those with more than 20 mitoses/10 HPF (P = 0.02), while those with 6-20 mitoses/10 HPF had an intermediate survival. The clinical and pathological features of patients with ILL suggest that this entity is closely related to PDLL and should be distinguished from WDLL.