A prospective study of comparable Japanese and British breast cancer patients treated by radical mastectomy confirmed previously reported findings that sinus histiocytosis and germinal center hyperplasia are more frequently seen in axillary lymph nodes from Japanese than in those from British patients. In Japanese, but not British, cases of either of these two morphologic findings had favorable prognostic significance for recurrence. Sinus histiocytosis also had favorable prognostic significance in Japanese cases for five year survival. In a separate review of axillary nodes from Japanese autopsy cases sinus histiocytosis was absent, suggesting that this finding in Japanese breast cancer cases was related to presence of the disease.