The clinical, haematological, morphological and histological features of a series of 22 patients presenting with splenic lymphoma with circulating villous lymphocytes were assessed and compared with those of patients with other forms of chronic B cell leukaemia in an attempt to differentiate this condition from hairy cell leukaemia, prolymphocytic leukaemia, and chronic lymphocytic leukaemia, with which this condition has many features in common. The disease was twice as common in men than in women, with a mean (SD) age at diagnosis of 72 (9) years, and the most consistent presenting feature was massive enlargement of the spleen, which showed white and red pulp disease with a plasmacytic component. Small monoclonal bands were found in 60% of cases.