BACKGROUND: Breast carcinoma survival rates were found to be higher in the U.S. than in Europe. METHODS: Multiple regression analysis of breast carcinoma survival rates among women diagnosed between 1990 and 1992 was performed using clinical data from population-based case series from the Surveillance, Epidemiogy, and End Results (SEER) program (13,172 women) and the European Concerted Action on survival and Care of Cancer Patients (EUROCARE) project (4478 women). RESULTS: Early-stage tumors (T1N0M0) were more frequent in the SEER data (41% of cases) than in the EUROCARE data (29%). In the SEER data, early tumors were more frequent in women age > or = 65 years (43%) than in younger women (38%), whereas the reverse was true in the European data (25% vs. 31%). In both case series, > 90% of women underwent surgery and 81-82% underwent lymphadenectomy, but the number of axillary lymph nodes evaluated was higher in the SEER data than in the EUROCARE data. The 5-year survival rate was higher in the U.S. case series (89%) than in the European series (79%). This differential was observed for each stage category evaluated: early (T1N0M0), large lymph node-negative (T2-3N0M0), lymph node-positive (T1-3N+M0), locally advanced (T4M0), and metastatic (M1) tumors. The overall relative excess risk (RER) of death was significantly higher (RER, 1.37; 95% confidence interval [95% CI], 1.25-1.50) among European women compared with U.S. women (referent group). Adjustment for stage, age, surgery, and the number of lymph nodes evaluated explained most of the excess risk (RER, 1.07; 95% CI, 0.98-1.17). CONCLUSIONS: Transatlantic differences in the 5-year survival rates for women diagnosed with breast carcinoma between 1990 and 1992 were attributable mainly to differences in stage of disease. Resources should be invested to achieve earlier diagnosis of breast carcinoma in Europe, especially for elderly women.