A study of 599 patients who had died of malignant lymphoma between 1952 and 1972 revealed involvement of the bladder in 13 per cent. Bladder involvement was always a secondary event, occurred in association with disseminated disease and was more common in non-Hodgkin's lymphoma than in Hodgkin's disease. Direct infiltration from adjacent pelvic foci as well as discrete apparent metastatic foci was noted. Involvement was usually microscopic although the presence of gross disease was invariably clinically manifest. Cystoscopy and cystography were valuable in the diagnosis of gross lesions. In contrast to primary vesical lymphoma the treatment of secondary vesical lymphoma was symptomatic and an operation was indicated rarely. Local radiotherapy was effective in treating the symptoms of secondary vesical lymphoma.