Eighty-eight patients with low grade non-Hodgkin's lymphoma were followed for a median period of 63 months. Sixty-eight per cent of the group were centrocytic/centroblastic B cell lymphomas by the updated Kiel classification. Fifty-one (58 per cent) of the patients were stage IV by the Ann Arbor classification. In 18 of these patients the bone marrow was the only site of extranodal involvement. Univariate survival analysis showed that the sum of involved sites was more discriminatory than Ann Arbor stage. Analysis by site of involvement showed that the liver and other intraabdominal sites were associated with worse survival than involvement of peripheral lymph nodes. Bone marrow and spleen involvement were not significantly associated with short survival. Increasing age at presentation was strongly associated with shorter survival and was also inversely correlated with serum albumin. Both low absolute lymphocyte count (< 1.0 x 10(9)/l), low serum IgG level (< 10 g/l) and low total immunoglobulins on presentation were significantly associated with short survival. Multivariate analysis showed that age, serum albumin and number of involved sites gave the best survival prediction. The sum of involved sites, immunoglobulin level and absolute lymphocyte count may be useful objective markers of prognosis in low-grade non-Hodgkin's lymphoma.