A case of a 71 years old, male patient, who was admitted to the hospital for lymphocytosis in the peripheral blood is presented. The diagnosis of B-cell chronic lymphocytic leukemia was established, based on the morphology and immunophenotypic analysis of lymphocytes of the peripheral blood. During diagnostic work-up the coexistence of a tumor in the right cardiophrenic angle was discovered at chest CT scan. Right thoracotomy and resection of the tumor was performed and biopsy revealed a mixed histology thymoma (AB according to the WHO classification). The association of thymoma with B-cell chronic lymphocytic leukemia is α very rare finding. Pneumon 2002, 15(3):319-322.