A 74-year-old man was diagnosed as having B chronic lymphocytic leukemia in June 1989. In 1940, when he was 25 years old, he was found to have tuberculoid leprosy and treated for 10 years. He subsequently received no therapy. As chronic stimulation by mycobacterium leprae might lead to malignant transformation in the lymphatic system, it was suspected that in this case leprosy may have played some role in the development of the chronic lymphocytic leukemia. However, no evidence to support such a hypothesis was obtained.