We report the diagnostic, prognostic and therapeutic features of non-Hodgkin's lymphoma in eight patients in whom the disease was seen as a primary tumor of the liver. This series illustrates the variety of situations in which lymphoma might be diagnosed: (a) abdominal pain and hepatomegaly (three cases), (b) incidental finding at evaluation of a patient with cirrhosis (two cases), (c) secondary neoplasm after treatment for Hodgkin's disease (one case) and (d) complication of AIDS (two cases). In most cases, clinical and/or radiological features were nonspecific. However, the combination of the following features must be considered as suggestive: occurrence of an apparently primary hepatic tumor in an immunocompromised patient, absence of the usual serum tumor markers and increased serum lactic dehydrogenase activity. The final diagnosis was based on histological examination of specimens obtained by ultrasonically guided liver biopsies or at surgery. All cases belonged to unfavorable histological subtypes. Immunohistochemical findings on paraffin-embedded sections demonstrated the B-lymphocyte lineage of the seven tumors available for study. In the three patients without coexisting disease, complete remission was obtained by surgery alone or combined with chemotherapy. In the two patients with coexisting cirrhosis, outcome was rapidly unfavorable, with death occurring less than 3 mo after diagnosis. Among the three immunocompromised patients, two experienced a rapid unfavorable outcome, and the remaining one was in complete remission after surgery and chemotherapy. In conclusion, primary non-Hodgkin's lymphoma of the liver arising in patients without coexisting disease has a slow progression and might be successfully treated by surgery.(ABSTRACT TRUNCATED AT 250 WORDS)