In the United States, Caucasian women are at higher risk of death from breast cancer than age-matched Japanese-Americans. The tumors of Japanese-Americans exhibit a greater uniformity of nuclear grade (NG), greater degrees of intratumoral lymphocytic infiltration (LI), and more conspicuous sinus histiocytosis (SH) in the regional lymph nodes. To assess the impact of histopathology upon the ethnic disparity in breast cancer mortality, we compared the survival experience of Japanese and Caucasian women with breast cancer in Hawaii. The study group consisted of 443 women, aged 45-74, whose cancers were diagnosed between 1975 and 1980. Survival status at 9 or more years after diagnosis, known for 416 of these women, was used in the analyses. Age and tumor stage at diagnosis were significant predictors of breast cancer death in the logistic regression analysis. When histopathological predictor variables (NG, LI, and SH) were included in the model, age, stage, NG, and LI were independently predictive. Although NG predicted stage among all patients, and SH predicted stage among the women with invasive disease, race was an independent predictor breast cancer stage in multivariate analyses. Finally, analysis within stage subgroups revealed that race was independently predictive of cancer death among women with localized disease (confined to the breast) but not among women with regional spread (local extension or axillary nodes involves). These results indicate that histopathological differences contribute to, but only partially explain, the disparity in breast cancer mortality between Caucasians and Japanese in Hawaii.