Forty six men with chronic lymphatic leukaemia (CLL) were studied for up to seven years. Six patients required surgery for prostatic outlet obstruction. Histological examination of the prostatic chippings showed variable degrees of infiltration with small mature lymphocytes in all six patients, suggestive of a leukaemic origin for the cells. Patients with chronic lymphatic leukaemia who undergo prostatectomy may have a higher incidence of leukaemic infiltration than has been previously recognised.