Pathologic features of 378 breast carcinomas without axillary lymph node metastases were correlated with long-term prognosis. Mitotic count, the feature best predicting prognosis, was most useful at lower mitotic count levels than usually studied. Cases with less than 4.5 mitotic figures per ten high-power fields had a 20-year tumor-related survival of 73% versus 48% for those with higher mitotic counts. Low and high mitotic count groups had significantly different prognoses for T1c, T2, and T3 tumors. Multivariate analysis showed that the best combination of features predicting tumor-related death were high mitotic count (relative risk, x 2.8), large tumor size (relative risk, x 1.7), lymphatic invasion (relative risk, x 1.7), and skin or subjacent muscle or chest wall invasion (relative risk, x 2.5). Nuclear grade, Bloom-Richardson grade, modified Scarff-Bloom-Richardson grade, Fisher's grade, and necrosis correlated well with survival but had no significant additional predictive value when adjusted for the mitotic count.